The  person  charging  this  material  is  re- 
sponsible for  its  return  to  the  library  from  I 
which  it  was  withdrawn  on  or  before  the  ; 
Latest  Date  stamped  below. 


Theft,  mutilation,  and  underlining  of  books 
are  reasons  for  disciplinary  action  and  may 
result  in  dismissal  from  the  University. 


UNIVERSITY  OF  ILLINOIS  LIBRARY  AT  URBANA-CHAMPAIGN 


BUILDING 


I 


L161  — 0-1096 


GROWTH  IN  SEEDLINGS  OF  PHASEOLUS  VUL- 
GARIS IN  RELATION  TO  , RELATIVE 
HUMIDITY  AND  TEMPERATURE 


BY 

CECIL  FREDERICK  PATTERSON 


B.  S.  A.  University  of  Toronto,  1918 
M.  S.  University  of  Illinois,  1 920 


THESIS 

Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the 

Degree  of 


DOCTOR  OF  PHILOSOPHY 


IN  BOTANY 


IN 


THE  GRADUATE  SCHOOL 


OF  THE 


UNIVERSITY  OF  ILLINOIS 


1921 


« « »•¥ 


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- . ii 


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<» 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


May  9, 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY  Cecil  Frederick  Patterson 

F.NTTTT.RD  Growth  in  Seedlii 
Relation  to  Relative  Humidity  aiid  Temperature 

BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  Doctor  of  Philoaophy. 


In  Charge  of  Thesis 


f 


Head  of  Department 


A 


Tr, 


Committee 


on 


Final  Examination* 


^Required  for  doctor’s  degree  but  not  for  master’s 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/growthinseedlingOOpatt 


TABLE  OF  CONTENTS. 


Page 

I , ACKNOWLEDGMENT  

II.  INTRODUCTION  1 

III.  REVIEW  OF  LITERATURE 7 

IV.  MATERIALS  AND  METHODS 14 

1.  Apparatus 15 

2.  Preparation  of  Seedlings 18 

V.  OUTLINE  OF  EXPERIMENTS 24 

VI.  PRESENTATION  OF  DATA 26 

1.  Growth  of  Seedlings  in  Continuous 

Darkness 27 

2.  Growth  of  Seedlings  in  Darkness 

Alternating  with  Light  40 

VII.  DISCUSSION 46 

VIII.  SUMMARY 59 

IX.  CONCLUSIONS 61 

X.  LITERATURE  CITED  62 

XI.  VITA 73 


I.  ACKNOWLEDGMENT. 


The  work  here  reported  was  performed  in  the  Laboratory 
of  Plant  Physiology,  University  of  Illinois,  under  the  direction 
of  Prof.  C.  F.  Hottes.  The  writer  feels  greatly  indebted  to 
Professor  Hottes  for  suggesting  the  problem  and  for  his  ever- 
ready  and  continuous  assistance  in  constructing  and  arranging 
the  apparatus.  His  suggestions  on  methods  of  experimentation 
and  on  working  up  the  data  are  fully  appreciated,  and  only 
through  his  efforts  and  his  encouragement,  during  the  course 
of  the  investigation,  has  the  material  here  presented  been  made 
available. 


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II.  INTRODUCTION. 

It  is  an  undisputed  fact  that  environmental  conditions 
play  an  important  role  in  determining  the  rate  of  growth  in 
plants.  Agriculturists,  horticulturists,  and  others  interested 
in  the  growing  of  plants  have  observed  that  certain  conditions 
of  environment  are  favorable  to  growth,  while  other  conditions 
are  unfavorable  and  retard  this  fundamental  life  process.  Dur- 
ing one  season,  plants  of  a given  species  thrive  and  produce  vig- 
orous growth,  while  during  the  season  following,  on  the  same 
soil  and  under  similar  cultural  conditions,  the  corresponding 
growth  rate  suffers  a marked  decrease.  In  a like  manner/  growth 
during  one  period  in  the  growing  season  may  be  more  rapid  by 
night  than  by  day,  while  during  another  period,  in  the  same  sea- 
son, the  reverse  may  be  true. 

As  to  what  factor  or  factors  are  responsible  for  the 
differences  in  the  responses  of  plants  to  the  physical  environ- 
ment little  is  known.  In  the  literature  on  plant  physiology^ 
some  of  the  differences  in  plant  response  have  been  attributed 
to  variations  in  definite  environmental  factors  with  little  or 
no  experimental  evidence  to  substantiate  the  conclusions  drawn. 
Plant  physiologists,  plant  ecologists  and  others,  in  studying 
growth,  have  noted  differences  in  the  behavior  of  plants  grow- 
ing under  different  sets  of  conditions  and,  in  many  cases,  have 
ascribed  the  differences  in  growth  to  a variation  in  one  factor 


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when  the  cause  might  reasonably  be  attributed  to  a variation 
in  several  factors.  In  such  cases  it  was  not  realized  that  the 
changing  of  one  environmental  factor  resulted  in  a changing  of 
two  or  more  factors.  For  instance,  Reinke  ('76),  in  early 
studies  on  plant  growth,  observed  that  a change  from  light  to 
darkness  was  usually  accompanied  by  an  increase  in  the  relative 
humidity.  The  conclusion  of  Brefeld  ('77)  that  the  formation  of 
the  pileus  in  Coprinus  depended  upon  the  presence  of  light  was 
found  to  be  in  error.  Lakon  ('07)  showed  that  excluding  the 
light  from  the  vessel  in  which  the  fungus  was  growing  changed 
the  temperature  and  the  relative  humidity  of  the  atmosphere 
surrounding  the  fungus.  Experience  has  shown  that,  in  nature, 
light,  temperature  and  relative  humidity  are  closely  interrelated 
and  that  the  condition  of  one  is  dependent,  in  a marked  degree, 
upon  the  condition  of  the  other  two.  As  the  light  decreases  in 
intensity  the  temperature  falls  and  reaches  a minimum  during  the 
hours  of  darkness.  With  this  fall  in  temperature  an  increase 
in  the  relative  humidity  follows.  On  the  return  of  light  the 
temperature  rises  and  a fall  in  the  relative  humidity  results. 

To  these  rapid  and  often  wide  changes  little  attention  has  been 
paid,  by  many  workers  in  the  field  of  plant  physiology. 

From  a study  of  the  plant  environmental  complex,  as  a 
whole,  it  may  be  seen  that,  in  growth  studies,  every  factor  must 
receive  due  consideration.  Jost  ('07)  recognized  that  the  daily 
periodicity  in  relative  humidity,  in  temperature  and  in  light, 
occurring  in  nature,  act  unequally  and  often  antagonistically 


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-3- 


upon  the  growth  processes*  The  same  authority  acknowledged 
that  it  was  impossible  to  interpret  growth  responses  as  affected 
by  three  variables  combined.  High  temperatures,  during  the  day, 
may  retard  growth  and  during  the  night,  when  the  temperature 
drops  to  near  the  optimum,  the  growth  rate  may  increase.  Like- 
wise^ conditions  may  exist  where  the  converse  is  true.  Still 
more  complex  is  the  problem  when  the  relationship  of  soil  temper- 
ature to  these  factors  and  to  growth  is  considered.  Free  ('ll) 
maintains,  "As  a part  of  the  surrounding  temperature  the  temper- 
ature of  the  soil  is  scarcely  less  important  than  that  of  the 
air".  On  the  other  hand,  Godlewski  has  shown  that  a drop  in  the 
soil  temperature  from  20.7  C.  to  5.5  C.  results  in  an  insignifi- 
cant decrease  in  the  growth  rate  of  the  shoot.  MaoDougal  ('03) 
has  shown  that  the  soil  temperature,  at  the  average  depth  for 
roots  of  herbaceous  plants,  reaches  a maximum  between  8 and  11 
o'clock  in  the  evening  and  a minimum  between  8 and  10  o'clock 
in  the  forenoon.  From  this  it  is  evident  that  when  the  atmospher- 
ic temperature  is  falling,  during  the  early  hours  of  the  night, 
the  relative  hujjidity  and  the  soil  temperatures  are  rising, 
and  v/hen  the  atmospheric  temperature  is  rising,  in  the  early 
part  of  the  day,  the  relative  humidity  and  the  soil  temperature 
are  falling. 

In  order  to  avoid  making  the  errors  so  common  in  much 
of  the  experimental  work  in  plant  physiology,  it  is  necessary  to 
carry  out  experiments  under  conditions  that  are  absolutely  under 
the  control  of  the  operator.  DeCandolle  ('05)  recognized  the 


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-4- 


importance  of  controlled  conditions  in  a study  of  plant  growth, 
and  in  an  address,  cited  by  Abbe  ( '05),  emphaaized  the  need  for 
plant  houses  in  which  the  various  environmental  factors  could  be 
controlled  and  changed  at  will.  This  need  received  the  endorse- 
ment of  Abbe  ('05)^  who  recognized  the  limitations  of  correlating 
field  observations  on  plant  grovrbh  with  climatic  data.  In  a re- 
cent work^ Livingston  (*17)  has  sounded  a note  of  warning  to  the 
investigator  and  has  drawn  attention  to  the  fact  that,  for  solv- 
ing the  fundaiuental  problems  in  growth,  an  environmental  control 
apparatus  is  indispensable. 

Only  recently  has  the  dream  of  DeCandolle  been  realized. 
For  some  years^ chambers  in  which  the  light  and  atmospheric 
temperature  factors  could  be  maintained  constant  or  changed  as 
desired  have  been  in  existence;  but  where  relative  humidity 
plays  a part  in  determining  the  growth  response,  the  usefulness 
of  such  chambers  is  limited.  In  the  plant  chambers  recently  de- 
vised by  Hottes  ('21), the  humidity  factor  also  is  under  control. 
These  chambers,  which  are  sufficiently  large  to  accomodate  higher 
plants  throughout  their  entire  growing  period,  are  so  arranged 
that  the  light,  temperature  and  moisture  factors  are  under  perfect 
control  of  the  investigator. 

From  a study  of  the  methods  of  experimentation  axiopted 
by  the  various  investigators  in  this  fieldjit  may  be  seen  that 
in  many  cases  the  conclusions  reached  are  unwarranted.  The  in- 
crease in  the  rate  of  elongation  in  shoots  of  sunflower  during 
darkness,  obtained  by  Reinke  ('76),  may  have  been  due  to  an  in- 


^P;  ■ : ; ::  ^lai 


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-5- 


crease  in  relative  humidity,  as  he  maintains;  but  since  the  en- 
vironmental factors  were  not  under  control,  temperature  may  have 
played  a part  in  bringing  about  this  change  in  the  growth  rate. 
The  agreement  of  the  growth  curve  in  Cucurbitaceous  fruits  with 
the  changes  in  relative  humidity,  observed  by  Clark  ('78),  Darwin 
('93)  and  Anderson  ('94)jmay  have  been  due  to  conditions  of  re- 
lative humidity  alone.  Since,  however,  the  periods  of  high  re- 
lative humidity,  recorded  by  them,  occurred  when  the  sun  was  ob- 
scured and  the  periods  of  low  relative  hiimidity  when  the  sun  was 
shining,  temperature  may  have  been  a very  important  factor  in- 
fluencing the  rate  of  enlargement.  The  increase  in  the  growth 
rate  in  Dendrocalamus  during  the  night  over  that  during  the  day 
at  Perad.eniya  and  Anuradhapura^  recorded  by  Smith  ('06),  suggests 
that  the  lower  temperatures,  obtaining  during  the  hours  of  dark- 
ness, were  more  favorable  to  growth  than  were  the  higher  ones 
characterizing  the  day,  and  that  this  increase  was  not  the  effect 
exclusively  of  an  increase  in  the  relative  humidity.  The  in- 
creases in  the  growth  rate  in  plants  during  darkness,  observed 
by  Sachs  ('74),  indicate  that  factors  other  than  light  may  have 
been  responsible,  in  part,  for  this  phenomenon. 

Owing  to  the  absence  of  proper  means  of  controlling 
the  environmental  factors  in  previous  investigations,  little 
is  known  absolutely  concerning  the  effect  of  relative  humidity 
on  growth  in  plant  shoots.  The  problems  in  growth  cannot  be 
solved  from  observations  on  plants  growing  under  fluctuating 
conditions  of  environment.  In  order  to  be  able  to  draw  correct 


71*,  ■•  ,-_^J  f>MW/Ww  • *'i'  1 - 


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■**  '■:  *•  » 


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obtained 

conclusions^ the  data  must  be^from  plants  growing  under  ifionditions 
where  each  individual  factor  of  the  environmental  complex  may 
be  maintained  constant  or  varied  at  the  wish  of  the  experimenter. 
The  variations  in  the  intensity  and  in  the  quality  of  light, 
occurring  in  nature,  must  be  eliminated;  the  fluctuations  in 
the  atmospheric  temperature  and  in  the  relative  humidity, 
characteristic  of  most  climates,  must  be  overcome;  the  soil 
temperature  and  the  soil  moisture  supply  must  be  under  the  con- 
trol of  the  investigator,  and  the  availability  of  the  food 
materials,  during  any  series  of  experiments,  must  be  maintained 
constant  before  a solution  to  the  factors  influencing  growth 
can  be  given. 

With  an  apparatus  for  controlling  both  root  and 
shoot  conditions  available, the  present  study  was  undertaken. 

This  study  was  designed  to  assist  in  clearing  up  the  divergent 
views  held  in  respect  to  growth  in  relation  to  relative  humidity 
and  temperature.  The  problem  is  large  and  the  working  of  it 
out  in  detail  will  require  a life  time.  In  the  present  work 
only  a beginning  has  been  made,  and  the  extent  of  the  investiga- 
tion was  limited  to  a study  of  growth  in  seedlings  subjected  to 
few  of  the  many  possible  combinations  of  environmental  conditions. 
The  major  part  of  the  investigation  was  carried  out  on  etiolated 
seedlings.  The  differences  in  their  response  to  humid  and  to 
dry  atmospheres  may  seem  insignificant,  but  it  should  be  remem- 
bered that  a beginning  must  be  madej  and  the  logical  point  of 
attack  is  in  seedlings  not  exposed  to  the  influences  of  light. 

In  the  minor  part  of  the  work,  which  consisted  in  a study  of 


/ 


1 


-7- 

illuminated  seedlings  in  the  presence  of  high  and  low  relative 
humidities,  less  significant  results  were  obtained.  Though 
very  limited  in  extent, the  latter  have  a direct  application  to 
growth  under  conditions  occurring  in  nature. 

III.  REVIEW  OF  LITERATURE. 

In  the  literature  on  plant  physiology^  much  may  be 
found  dealing  with  the  influence  of  temperature  upon  growth  in 
mmitm  plants.  The  studies  of  Sachs  (*60,  *74,  *9S),  Koeppen 
(*75),  Reinke  (*76),  Askenasy  (*90),  Godlewski  ('91,  *93),  Ward 
(*95),  True  (’95),  Balls  (’08),  Lehenbauer  (’14)  and  others  have 
given  to  us  a knowledge  of  the  basic  laws  governing  growth  in 
relation  to  temperature.  The  humidity  relations,  on  the  other 
hand,  have  been,  in  a large  degree,  overlooked.  It  is  true  that 
authors  have  made  reference  to  high  relative  h-umidity  as  a fac- 
tor increasing  the  growth  rate,  but  little  absolute  experimental 
evidence  is  available.  The  growth  rate  has  been  changed  with 
a change  in  the  relative  humidity,  but  in  many  cases,  it  is 
evident  that  the  relative  humidity  was  very  imperfectly  con- 
trolled and  that  the  humidity  changes  were  accompanied  by  changes 
in  other  environmental,  factors. 

One  of  the  earliest  attempts  to  determine  the  effect 

of  relative  humidity  on  growth,  recorded  in  literature,  is  that 

respective  rates 

of  Reinke  (’76).  This  author  compared  the^growth^6£  potted 
plants  of  sunflower  (Helianthus  annuus)  placed  near  a window. 


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one  under  a bell  jar  and  one  in  the  free  circulating  atmosphere 
of  the  laboratory.  He  observed  that  the  growth  rate  in  the 
plant  under  the  bell  jar  was  much  greater  than  that  of  the  plant 
in  the  free  air.  This  increase  in  the  growth  rate  exhibited 
by  the  plant  under  the  bell  jar  was  due,  he  believed,  to  the 
higher  relative  humidity  obtaining  in  the  atmosphere  surround- 
ing the  plant.  Where  the  humidity  was  not  controlled,  growth 
during  darkness  exceeded  that  during  light.  Later,  he  was  able 
to  show  that  under  conditions  of  constant  relative  humidity 
growth  in  plants  exposed  to  light  was  more  rapid  than  that  in 
the  same  plants  maintained  in  darkness.  He  explains  this  dis- 
crepancy on  a basis  of  h higher  relative  humidity  obtaining 
in  the  absence  of  light.  In  further  investigations,  he  found 
that  growth  in  thickness  in  stems  of  Datura  was  proportional 
to  the  relative  humidity  and  that  Datura  leaves  exhibit  a more 
gapid  growth  by  night  than  by  day.  This  latter  observation  can 
be  accounted  for,  he  maintains,  by  the  existence  of  a higher 
relative  humidity  during  the  hours  of  darkness  than  during  the 
hours  of  light. 

The  researches  of  Sorauer  ('80)  on  summer  barley  show 
that  with  an  increase  in  the  relative  humidity  an  increase  in 
the  rate  of  elongation  results.  The  plants  grown  in  a dry 
atmosphere,  however,  were  stockier  and  possessed  greater  fresh 
and  dry  weights  than  did  those  grown  in  a humid  atmosphere. 
Later,  the  same  author  reports  results  obtained  from  subjecting 


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plants  of  Pyrus  communis,  Vitis  vinifera,  Ailanthus  glandulosus 
and  Lupinus  luteus  to  dry  and  to  humid  atmospheres.  His  observa- 
tions show  that  in  plants  of  some  species  a humid  atmosphere 
accelerates  growth,  while  in  plants  of  other  species  growth 
takes  place  more  rapidly  in  the  presence  of  a dry  atmosphere. 

In  Lupinusjthe  plants  grown  in  a. humid  atmosphere  possessed 
longer  stems  and  greater  fresh  weights  than  did  the  plants  grown 
in  a dry  atmosphere.  The  plants  grown  in  a dry  atmosphere, how- 
ever, possessed  the  greater  dry  weight. 

Reinitzer  (*81)  demonstrated  that  atmospheric  humidity 
plays  3 significant  role  in  determining  the  rate  of  elongation 
in  plant  shoots.  By  subjecting  shoots  of  Evonymus  japonicus, 
Tradescantia  viridis  and  Nerium  oleander  to  dry  and  to  humid 
atmospheres,  he  observed  that  the  rate  of  elongation  in  the 
humid  atmosphere  was  from  two  to  four  times  as  rapid  as  that 
in  the  dry  atmosphere. 

In  pea  seedlings  Vesque  and  Viet  (*61)  observed  a 
great  difference  between  the  growth  rates  in  dry  and  moist 
atmospheres,  respectively.  Without  exception, elongation  in 
roots  took  place  more  rapidly  in  a humid  atmosphere  than  in 
a dry  atmosphere.  In  shootsjthis  was  true  in  the  case  of  one 
plant  only.  Taking  the  average  values,  elongation  in  shoots  . 
proceeded  more  rapidly  in  a dry  atmosphere  than  in  a humid 
atmosphere,  while  in  roots  the  converse  was  true. 

Hellriegel  (*83)  demonstrated  that  under  favorable 
conditions  of  soil  moisture  a low  relative  humidity  may  be  not 


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less  favorable  to  growth  than  a high  relative  humidity.  Plants 
of  barley,  grown  in  a soil  whose  moisture  content  varied  from 
30  to  60  per  cent  saturation,  made  as  rapid  growth  in  the  pres- 
ence of  a dry  as  in  the  presence  of  a moist  atmosphere.  He 

ft  * 

states  "Diese  Anderung  der  Verdunstungsgr6sse  tLbt  aber  keinen 
Einfluss  auf  die  physiologischen  Funktionen  der  Pflanzen,  auf 
ihre  Produktion  und  Gesamtentwickelung  aus,  so  lange  die  Boden- 
feuchtigkeit  innerhalb  normaler  und  gflnstiger  Grenzen  erhalten 
wird". 

The  researches  of  Brenner  (’00)  on  Snmpervivum 
assimile  and  on  Sedum  dasyphyllum,  indicate  that  a high  relative 
humidity  brings  about  an  excessive  elongation  in  plant  shoots. 
According  to  this  author, plants  grown  under  very  humid  condi- 
tions resemble,  in  respect  to  height,  those  grown  in  the  absence 
of  light.  In  Sedum, he  observed  that  at  distances  of  1.5  meters 
and  5.0  meters  from  a window  and  in  the  free  air  seedlings  made, 
in  a period  of  14  days,  a growth  of  from  3 to  6 millimeters 
and  from  6 to  14^  millimeters,  respectively.  At  the  same  distances 
and  during  a period  of  similar  length,  but  under  a bell- jar, 
they  made  a growth  of  from  5 to  8 millimeters  and  of  from  10  to 
20  millimeters,  respectively. 

Unlike  the  results  of  Brenner  are  those  obtained  by 
Schaible  (*01).  This  investigator  exposed  potted  plants  of  the 
bean  (Phaseolus  vulgaris)  and  plants  of  the  same  species,  grow- 
ing in  nutrient  solutions,  to  a dry  atmosphere  and  compared  the 
growth  rate  in  these  plants  with  the  growth  rate  of  similar 


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-11- 


plants  growing  in  an  atmosphere  charged  with  moisture.  In  one 
series  the  atmospheric  pressure  remained  normal,  while  in  another 
it  was  reduced  to  one-fourth  normal.  Under  both  conditions  of 
atmospheric  pressure^ the  growth  rate  was  more  rapid  (and  the 
leaves  larger)  in  the  plants  grown  in  the  drier  atmosphere.  He 
states,  "Nach  diesen  Resultaten  hatte  die  Luftfeuchtigkeit  kein- 
en  Einfluss  gehabt". 

On  a basis  of  dry  weighty  Ts chap lowitz  ('66)  found 
that  seedlings  of  Pisum  sativum  growing  in  a dry  atmosphere 
exhibited  a growth  rate  unlike  that  of  seedlings  of  the  same 
species  growing  in  a humid  atmosphere.  He  states,  "Wie  Zahlen 
ergeben  betragt  das  Gewicht  der  absolut  trocknen  Pflanzen- 

X 

substanz  der  oberirdischen  Organe  der  in  den  HSus^  mit  der 
hOhern  DunstsEttigung  (63  und  47^  der  relativen  Feuchtigkeit) 
gewaohsenen  Pfianzohen  bedeutend,  nahezu  14%,  mehr,  als  das 
der  betreffenden  Organe  der  in  den  trockneren  Vegetations- 
raumen  (mit  46  und  39%  der  relativen  Feuchtigkeit)  erzogenen 
jungen  Erbsenpflanzen" . 

In  plants  of  Phaseolus  multiflorus^Godlewski  (’91) 
observed  that  an  abrupt  decrease  in  the  growth  rate  resulted 
when  the  plants  were  changed  suddenly  from  an  atmosphere 
possessing  a relative  humidity  of  64  per  cent  to  one  possessing 
a relative  h\imidity  of  38  per  cent.  This  increase  in  the  rate 
of  elongation,  however,  persisted  for  a short  time  only,  and 
the  growth  rate  soon  assumed  its  former  value.  On  increasing 
the  relative  humidity  from  38  per  cent  to  87  per  centra  sudden 


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-12- 


inorease  in  the  growth  rate  resulted,  but  this  increase  was  of 
short  duration.  After  two  hours  the  growth  rate  in  the  higher 
relative  humidity  was  approximately  equal  to  that  in  the  lower 
relative  humidity.  He  believed  that  these  changes  in  the 
growth  rate  were  due  to  purely  physical  causes  and  that  they 
could  be  explained  on  a basis  of  turgor  relations.  He  says, 
however,  "Die  epikotylen  Glieder  der  Pflanzen,  welche  in  be- 

s 

standig  feucht  gehaltener  Atm<^hftre  verweilen,  waohsen  dber- 
haupt  bedeutend  schneller  und  erreichen  eine  bedeutend  grdssere 
finale  Lftnge  ala  die  der  Pflanzen  welche  unter  sonst  Shnlichen 
Bedingungen  in  einer  trockenem  AtmosphAre  gezogen  werden". 

The  researches  of  Clark  (‘78),  Anderson  (*94)  and 
Darwin  (*93)  give  support  to  the  conclusions  reached  by  God- 
lewski.  Their  investigations  show  that  relative  humidity  is 
an  important  factor  in  determining  the  rate  of  development 
in  fruits  of  Cucurbita.  They  have  demonstrated  that,  at  times, 
the  rate  of  enlargement  increases  or  decreases  as  the  relative 
humidity  becomes  higher  or  lower.  Clark,  in  studying  the 
expansive  power  of  a developing  fruit  of  this  genus,  observed 
that  the  pressure  was  greatest  during  the  early  hours  of  the 
morning.  This,  he  believed,  was  due  to  the  presence  of  a high 
relative  humidity  during  those  hours.  Anderson  and  Darwin  made 
careful  hourly  weighings  of  developing  fruits  and  correlated 
the  hourly  increments  with  the  conditions  of  temperature  and 
relative  humidity  for  the  corresponding  period.  Their  curves 
for  weight  increase  follow  , in  a general  way,  the  curves  for 


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relative  humidity.  At  times  this  correspondence  was  perfect. 

At  other  times,  however,  the  data  suggest  that  some  factor 
or  factors,  other  than  relative  humidity,  were  operating  in 
limiting  growth. 

An  attempt  to  study  growth  in  relation  to  atmospheric 
humidity,  in  a systematic  way,  was  that  of  Wollny  (*98).  His 
reseaJTches  in  this  connection  were  confined  to  plants  of  bar- 
ley, vetch,  lucerne,  flax  and  potato.  In  general,  an  increase 
in  the  relative  humidity  brought  about  an  increase  in  the  rate 
of  stem  elongation  and  an  increase  in  the  production  of  plant 
substance,  both  fresh  and  dry. 

One  of  the  most  extensive  investigations  on  growth 
in  plants,  in  relation  to  relative  humidity,  was  carried  out 
by  Eberhardt  ('03,  '04),  Plants  of  many  species,  including 
Lupinus  albus.  Mimosa  pudica,  Phaseolus  vulgaris,  Faba  vulgaris. 
Coleus  blumei,  Ricinus  communis  and  others,  were  subjected  to 
three  different  conditions  of  relative  humidity,  namely,  "Humid", 
"Normal",  and  "Dry"..  The  plants  maintained  in  the  "Humid" 
atmosphere  consistently  made  greater  growth  increments  than  did 
those  maintained  in  either  a "Normal"  or  in  a "Dry"  atmosphere. 
Likewise^ with  but  one  exception,  did  the  plants  maintained  in 
a "Normal"  atmosphere  make  greater  elongation  increments  than 
those  maintained  in  a "Dry"  atmosphere. 

Similar  to  the  observations  of  Clark  ('78),  Anderson 
('94)  and  Darwin  ('93)  were  those  of  Lock  ('04)  and  Smith  ('06), 

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-14- 


Smith  observed  that  the  growth  curve  in  plants  of  Dendro- 
oalamus  giganteus  followed  closely  the  curve  for  relative 
humidity  during  the  day  at  Hakgala  and  during  the  day  and  part 
of  the  night  at  Peradeniya  and  Anuradhapura.  In  shoots  of 
Capparis,  Stifftia  and  Eranthemum  oinnabarinum  the  growth  rate 
during  the  day  showed  a close  correspondence  with  the  relative 
humidity.  Measurements  of  fruits  of  Artocarpus  integrifolia, 
taken  twice  daily,  morning  and  evening,  indicate  a much  higher 
rate  of  enlargement  during  the  night  than  during  the  day.  This^ 
he  believed,  was  due  to  the  presence  of  a higher  relative  humidity 
during  the  hours  of  darkness.  Lock’s  observations  on  Dendro- 
calamus  giganteus,  Gigantochloa  aspera  and  Bambusa  spinosa  were 
similar  to  those  of  Smith.  Rate  of  elongation  in  shoots  of  these 

O 

species,  was  found  to  follw  closely  the  fluctuations  in  the 

A 

amount  of  moisture  present  in  the  atmosphere. 

IV.  MATERIALS  AND  METHODS. 

The  experimental  work  upon  which  this  paper  is  based 
w^s  carried  out  on  seedlings  of  the  common  bean  (Phaseolus  vul- 
garis) during  the  winter  months  of  the  years  1930  - 1921.  Two 
adjoining  sections  of  a glass  house,  in  which  the  heating  was 
under  thermostatic  control,  were  appropriated  for  the  purpose 
of  carrying  on  the  investigation.  Through  a system  of  ventila- 
tion in  combination  with  steam  heating,  the  room  temperature  was 
maintained  easily  within  the  desired  range.  The  excess  light. 


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-15- 


on  sunny  days,  was  excluded  by  a coating  of  green  paint  applied 
to  the  inndr  surface  of  the  roof,  and  where  necessary  the  plant 
chambers  were  protected  by  light  shades. 

1.  Apparatus. 

The  various  forms  of  apparatus  used  by  previous  in- 
vestigators in  attacking  this  problem  have  been  of  a very  im- 
perfect type, and  the  conditions  as  stated  in  their  reports  are, 
at  the  best,  only  approximately  correct.  Brenner  (*00),  Eber- 
hardt  (‘03,  '04),  Hellriegel  ('83),  Reinitzer  ('81),  Reinke  ('76), 
Schaible  ('01),  Sorauer  ('80)  and  Vesque  and  Viet  ('81)  employed 
bell- jars,  while  Godlewski  ('91),  Wollny  (*98)and  Bovie  ('10) 
employed  chambers  in  which  to  grow  the  plants  during  the 
period  of  observation.  The  atmosphere,  in  the  bell- jars  or  in 
the  chambers,  was  maintained  either  dry  or  wet  by  passing  the 
air,  as  it  entered  the  enclosed  areas,  over  sulphuric  acid  or 
calcium  chloride,  or  through  water.  To  further  assist  in  re- 
moving the  moisture, Sorauer  placed  open  dishes  containing 
sulphuric  acid  under  the  bell- jars,  and  Schaible  relied  on 
this  method  entirely.  A few  workers  have  given  the  actual 
values  expressing  the  relative  humidity  obtaining  at  the  time; 
while  others  have  merely  stated  that  the  atmosphere,  in  which 
the  plants  were  growing,  was  dry  or  moist.  In  no  case,  among 
the  investigations  cited,  was  the  relative  humidity  under  auto- 
matic control. 

Since  it  was  desired,  during  some  of  the  present 




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-16- 


experiments,  to  maintain  the  temperature  of  the  root  at  one 
point  and  that  of  the  shoot  at  another,  it  was  necessary  to  em- 
ploy an  apparatus  by  which  the  temperature  of  the  root  could  be 
controlled  independently  of  that  of  the  shoot.  Preliminary  ex- 
periments showed  that  this  could  well  be  done  by  utilizing  a con- 
stant temperature  water-bath, in  maintaining  the  temperature  of 
the  root,  and  a combined  temperature  and  hxamidity  chamber  in 
the  control  of  the  environmental  factors  of  the  shoot. 

Water-baths.  The  water-baths  used  in  maintaining  the 

# 

root  temperatures  consisted  of  galvanized  iron  tanks,  20  inches 
in  width,  7 inches  in  depth  and  from  3 to  7 feet  in  length,  filled 
with  water  to  the  desired  level.  Heating  of  the  water  was 
effected  by  electric  heaters,  two  in  each  tank,  under  the  control 
of  a thermo- regulator.  The  temperature  of  the  water  was  maintain- 
ed uniform  throughout  by  a system  of  aeration. 

Covering  each  bath  was  a sheet  of  an  asbestos  compound, 
known  commercially  as  "Transits”.  In  each  sheet, openings  were 
made  for  the  accomodation  of  the  plant  shoots  and  for  the  lead 
tubing  which  conducted  the  air  to  the  baths  for  purposes  of 
agitation.  In  one  of  the  sheets  covering  each  tank, two  additional 
openings  were  drilled,  one  for  the  thermo-regulator,  and  the 
other  for  a cork  supporting  a thermometer.  The  openings  for  the 
plant  shoots  were  nine  in  number  and  measured  one  and  one-fourth 
inches  in  diameter.  These  openings  were  arranged  in  the  form 
of  a square,  with  a distance  cf  four  and  one-half  inches  from 


centre  to  centre. 


-17- 


Plant  chambers  and  air-conditioning  apparatus.  The 
plant  chambers  and  the  air-conditioning  apparatus,  employed 
for  controlling  the  environment  of  the  plant  shoots,  were 
essentially  the  same  as  those  described  in  detail  by  Hottes 
(’21).  During  these  experiments,  however,  the  walls  and  the 
door  of  the  chambers  were  rendered  opaque  by  a covering  of 
heavy  paper  boards. 

Since  a means  for  cooling  the  atmosphere  in  the  plant 
chambers  was  not  provided,  it  was  necessary  to  take  special 
precautions  that  the  temperature  of  the  air  in  the  room  did 
not  exceed  the  temperature  of  the  air  in  the  plant  chambers. 

The  temperature  of  the  rooms  was  kept  down  by  adjusting  the 
thermo-regulator  to  give  low  heat  and  by  ventilation  on  sunny 
days,  when  the  air  temperature  in  the  house  was  likely  to 
exceed  the  maximum  desired  in  the  plant  chambers. 

The  apparatus,  arranged  as  indicated,  worked  admirably 
well  and  gave  highly  satisfactory  results.  The  thermo-regula- 
tors and  hum i do- regulators  proved  very  sensitive  to  heat  and 
moisture,  respectively.  With  these  instruments  properly  adjusted, 
the  atmospheric  conditions  in  the  plant  chambers  were  main- 
tained constant  to  a marked  degree.  In  respect  to  temperature, 
the  variation  from  the  mean  was  kept  at  a value  less  than  .5*0. 
Records,  given  by  a humidograph,  show  that  the  hum i do- regulator 
is  capable  of  maintaining  a relative  humidity  with  a fluctuation 
of  less  than  2 per  cent.  To  avoid  making  unnecessary  claims. 


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-la- 


the variation,  during  this  investigation,  may  be  put  at  a 
value  not  to  exceed  5 per  cent  - two  and  one-lfialf  per  cent 
in  either  direction  from  the  mean.  A variation  of  5 per  cent 
in  the  relative  humidity  is  not  excessive  and,  within  the  limits 
of  these  experiments,  is  as  little  as  could  be  desired. 

3.  Preparation  of  Seedlings. 

As  previously  stated,  seedlings  of  the  common  bean 
served  as  plant  materials  for  experimentation.  Seedlings  of 
this  species  were  chosen,  owing  to  the  ease  with  which  they  can 
be  grown  and  to  their  great  adaptability  to  laboratory  methods. 
The  seeds  were  of  the  Red  Valentine  variety  and  were  obtained 
from  the  Burpee  Seed  Company. 

To  insure  seedlings  of  uniform  vigo:>the  researches  of 

Blanchard  (*10),  Bolley  (’01),  Clark  (’04),  Cobb  (’03),  Cum- 

\ 

mings  (’14),  Desprez  (’95),  Fruwith  (’17),  Grenfell  •( ’01) , 
Haberlandt  (’66),  Hicks  and  Dabney  (’96),  Kiesselbach  (’17), 

Love  (’12),  Lyon  (’05),  Miller  and  Pammel  (’01),  Montgomeiy( *08, 
*12),  Sanborn  (’92),  Shamel  (’05),  Shaw  (’06),  Snyder  (’05), 

Soul  and  Vanatter  (’01,  ’03),  Walls  (*05),  Webber  and  Boykin 
(’07),  Williams  (’03,  *05),  Wollny  (‘77,  ’87)  and  others  (Kidd 
ajid  West,  *18,  *19)  show  the  necessity  for  employing  seeds  of 
uniform  size.  Though  the  investigations  of  Middleton  (’99) 
indicate  that,  in  the  bean,  size  of  seed  has  little  influence  on 
the  resulting  plants,  the  evidence  appears  to  be  in  favor  of 
the  conclusions  reached  by  the  former  mentioned  investigators. 
Accordingly,  the  sample  of  seed,  taken  at  random  from  a large 


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-19- 


supply,  was  divided  into  three  grades,  on  a hasis  of  length, 
by  employing  a measuring  caliper.  The  first  grade  included 
seeds  more  than  17  millimeters  in  length;  the  second  those 
between  13  and  17  millimeters  in  length;  and  the  third,  all 
those  below  13  millimeters  in  length.  For  the  present  study^ 
seeds  belonging  to  the  second  group  were  chosen. 

In  order  to  determine  the  relation  between  reserve 
(food  supply)  and  growth,  under  the  various  conditions  of  mois- 
ture and  temperature  employed,  each  bean  was  weighed  individually 
and  its  weight  recorded  to  the  second  decimal  place  in  grams. 

The  beans  were  germinated  at  room  temperature,  in  moist  sand, 
in  a germinating  pan.  Upon  the  radicles  reaching  a length  of 
from  2 to  3 centimeters, the  seedlings  possessing  radicles 
showing  a small  departure  from  the  mean, in  respect  to  length, 
were  transferred  to  one-quart  Mason  jars  containing  the  desired 
culture  medium. 

As  a medium  a white  silica  sand,  brought  to  the  de- 
sired moisture  content  by  the  addition  of  water  from  the  Uni- 
versity wells,  was  employed.  The  sand  is  almost  a pure  silica, 
and  the  water  is  in  itself  a well  balanced  nutrient  solution, 
as  shown  by  the  following  analysis,  furnished  by  the  Illinois 
State  Water  Survey  (’15): 


Mineral 

salts 

KNO^ 

KCl^ 


Parts  per 
million 


2.3 

.8 

2.0 

6.4 
81.7 

7.5 


Mineral 

salts 


MgCOa 

CaCO, 

FeCO^ 


Parts  per 
million 
105.3 
144.8 


Bases 

Total 


375.0 


4.4 
. 6 

15.8 

3.4 


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-30- 


To  overcome  the  difficulty  experienced  by  Briggs 
and  Shantz  ('13),  Kiesselbach  (*15),  Montgomery  ('13),  Living- 
ston ('18),  Brenchley  ('30)  and  others  in  maintaining  a medium 
uniform  throughout,  in  respect  to  moisture,  the  sand  was  brought 
up  to  the  desired  moisture  content  before  putting  it  in  the  jars 
and  undue  evaporation  prevented  during  the  development  of  the 
seedlings.  The  respective  moisture  contents  were  obtained  by 
mixing  together,  in  a large  bowl,  a known  weight  of  dry  sand 
and  the  correct  amount  of  water.  The  weight  of  water  required 
in  a given  case  was  determined  from  the  value  representing  the 
water  holding  capacity  of  the  sand,  as  ascertained  by  a modifi- 
cation of  the  Hilgard  method  (Hilgard,  'l9)»  Preliminary  ex- 
periments showed  that,  with  ample  precautions,  the  loss  of  water 
from  the  sand  in  the  jars  during  the  growing  period  of  the 
seedlings  did  not  exceed  4 per  cent  of  the  sand's  total  water 
holding  capacity.  To  offset  this  loss^the  moisture  content  of 
the  sand,  at  the  time  of  mixing,  was  made  to  exceed  the  stated 
value  for  each  series  of  experiments  by  from  1 to  3 per  cent. 

This  treatment  provided  a sand  with  an  average  moisture  content, 
throughout  the  period  of  experimentation,  equal  to,  approximately, 
the  values  given  in  the  tables.  For  instance,  in  the  series 
run  in  a soil  moisture  of  30  per  cent  saturation  and  in  an 
atmospheric  relative  humidity  of  30  per  cent,  the  moisture  con- 
tent of  the  sand,  at  the  time  of  mixing,  was  made  up  to  33  per 
cent.  At  the  close  of  the  experiment  this  value  was  found  to 
be  approximately  18  per  cent.  The  average  for  the  period, 
therefore,  was  30  per  cent. 


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-21- 


To  secure  uniform  compactness  in  the  aand,  the 
jars  were  filled  loosely  with  the  moistened  sand  and  were 
allowed  to  drop  a set  distance  on  a padded  board  a definite 
number  of  times.  After  this  operation  the  jars  were  refilled 
and,  with  a slight  pressure  of  the  hand,  the  level  of  the  sand 
brought  to  the  desired  distance  below  the  top.  The  germinated 
seeds  were  set  one  in  each  jar,  at  uniform  depths  below  the 
surface  of  the  medium.  A metal  cover,  with  a small  perforation 
to  peimiit  exchange  of  gases,  was  placed  over  each  jar.  The 
cultures,  thus  prepared,  were  enclosed  between  two  circular 
pans.  The  cultures  were  set  in  one  pan,  which  contained  a 
small  amount  of  water,  and  the  other  pan  was  inverted  to  form 
an  enclosure.  The  water  in  the  lower  pan  was  provided  to  in- 
crease the  atmospheric  humidity  surrounding  the  cultures,  in 
order  to  prevent  excessive  evaporation  from  the  sand  in  the  jars. 
When  the  cotyledons  appeared  above  the  surface  of  the  sand^the 
small  metal  covers  were  removed  from  the  jars,  but  the  cultures 
were  retained  within  the  pan  enclosure  until  ready  for  trans- 
ference to  the  water-bath.  In  all  oases, twice  the  required 

\ 

number  of  seedlings  were  prepared,  in  order  that  those  exhibi- 
ting malformations  and  that  those  showing  marked  departures 
from  the  average,  in  respect  to  growth  rate,  might  be  eliminated. 

Upon  the  seedlings  reaching  a height  of  about  4 
centimeters, the  required  number  for  experimentation  was  select- 
ed, taking  those  that  showed  uniformity  in  height,  and  prepared 
for  the  baths.  To  the  top  of  each  jar  was  secured  a metal 


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-23- 


secured  by  paper  clips  to  a metal  strip  supported  by  the  wire 
upright.  The  seedling  was  held  in  contact  with  the  combined 
scale  and  support  by  a small  rubber  band,  sufficiently  large 
to  bring  only  very  slight  pressure  to  bear  on  the  shoot.  As 
a precautionary  measure  against  the  stimulation  of  growth, 
through  the  agency  of  contact,  the  rubber  band  was  placed  well 
below  the  growing  zone. 

With  this  arrangement  the  heights  of  the  seedlings 
were  read  with  ease.  During  the  early  stages  of  growth^ the 
readings  were  obtained  through  the  small  openings  in  the  base 
of  the  chamber,  provided  by  the  doors  in  the  condulet  covers. 

In  the  later  stages  of  elongation, the  readings  were  obtained 
through  a large  glass  door,  with  which  each  chamber  was  pro- 
vided. 

After  the  transference  of  the  cultures  to  the  baths_^ 
a period  of  from  2 to  6 hours  elapsed  before  the  first  readings 
were  obtained.  This  was  permitted^in  order  that  the  seedlings 
might  become  accomodated  to  their  new  environment.  Readings 
on  shoot  elongation  were  obtained  twice  daily,  with  a period  of 
12  hours  between  readings,  and  the  increments  in  the  hypocotyls 
and  in  each  internode  were  recorded  separately.  At  about  three- 
hour  intervals,  from  7 A.M.  to  10  P.M.  readings  on  temperature 
and  on  relative  humidity  were  obtained.  In  this  way  a close 
check  was  kept  on  the  behavior  of  the  thermo-regulator  and  the 
humido-regulator.  Occasionally  an  instrument  failed  to  respond. 


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-22- 


coger  provided  with  a short  bEass  tube,  centrally  located  and 
of  sufficient  size  to  permit  the  passage  of  the  cotyledons  and 
bent  hypocotyls.  After  putting  the  cover  in  placej-the  opening 
in  the  tube  surrounding  the  shoot  was  sealed  with  plastic  clay, 
The  cultures  were  then  labelled  and  the  weight  of  each  ;jar  and 
its  content^^S’ecorded. 

At  this  stage  the  cultures  were  in  readiness  for 
transference  to  the  water-baths.  These  baths  were  situated, 
as  already  indicated,  below  the  plant  chambers.  To  permit  this 
transfer^  the  plant  chamber,  with  its  base,  was  elevated  by  rope 
and  pulleys, and  the  sheet  of  "Transits”,  which  served  as  a cover 
for  the  tank  and  as  floor  for  the  chamber,  was  removed.  The 
cultures  were  then  put  in  position,  nine  below  each  chamber. 

The  water  of  the  bath  was  brought  to  a level  of  about  one  inch 
below  the  top  of  the  jars,  and  the  sheet  of  "Transits"  replaced. 
To  prevent  the  entrance  of  moisture  to  the  plant  chamber  from 
the  bath  below,  the  joints  were  sealed  with  plastic  clay.  After 
replacing  the  chamber  and  its  base^the  growth  measuring  scale 
and  the  supports  for  the  seedlings  were  put  in  place. 

The  support  for  each  seedling  consisted  of  a heavy- 
iron  washer,  to  which  was  riveted  an  upright  of  No.  9 galvanized 
wire.  In  addition  to  offering  support  for  the  seedlings,  these 
uprights  served  to  support  a millimeter  scale,  from  which  the 
height  of  the  seedlings  was  read  directly.  The  scale  consisted 
of  a narrow  section  of  millimeter  cross-section  paper,  which  was 


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-24- 


In  such  cases  the  data  obtainedwere  discarded  and  the  ex- 
was 

periment  repeated.  Observations  on  each  lot  of  seedlings 
were  continued  until  the  shoots  ceased  elongating. 

After  elongation  in  the  shoots  came  to  an  end^the 
cultures  were  removed  from  the  baths  and  weighed.  The  seedlings 
were  then  removed  from  the  jars,  and  care  was  talten  to  secure 
the  entire  root  system  of  each  plant.  The  particles  of  sand, 
clinging  to  the  roots,  were  removed  by  washing  in  water.  Be- 
fore weighing,  the  excess  water  adhering  to  the  roots  was 
removed  by  the  aid  of  dry  cloths.  Immediately  following  this 
washing  and  drying,  the  fresh  weight  of  each  root  and  shoot 
was  determined  and  recorded  separately.  After  drying  for  24 
hours  at  a temperature  of  30**C. , these  products  were  trans- 
ferred to  a high  temperature  oven  (96*C.)  and  there  dried  to 
constant  weight.  With  the  dry  weight  determined^ the  securing 
of  data  was  completed. 

V.  OUTLINE  OF  EXPERIMENTS. 

For  convenience, the  experiments  are  treated  under 
two  sections: 

1#  Growth  of  seedlings  in  continuous  darkness. 

2..  Growth  of  seedlings  in  darkness  alternating 

with  light. 

As  already  stated, the  major  part  of  the  investigation 
was  carried  out  on  non- illuminated  seedlings.  These  seedlings 


»■ 

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-25- 


were  grovm  under  different  conditions  of  temperature,  relative 
humidity  and  soil  moisture.  The  conditions  obtaining  at  any 
one  time,  however,  were  maintained  constant  during  the  series. 
Lack  of  time  prevented  the  using  of  more  than  one  root  temper- 
ature, but  two  shoot  temperatures,  three  relative  humidities 
and  three  soil  moistures  were  employed.  The  root  temperature, 
in  all  experiments,  was  maintained  at  25  C.  The  other  environ- 
mental conditions  were  changed,  when  desired,  giving  the  follow- 
ing combinations: 

Shoot  temperature  Soil  moisture  Relative  humidity 
( C.)  (per  cent  (per  cent) 

saturation) 


5 

30 

60 

90 

20 

30 

60 

90 

60 

30 

60 

90 

5 

30 

60 

90 

20 

30 

60 

90 

60 

30 

60 

90 

The  seedlings,  included  in  the  experimental  work  of 
Part  II,  were  illuminated  from  7 A.M.  to  7 P.M.  Illumination 
was  provided  by  light  from  the  natural  source,  entering  the 
plant  chamber  through  a glass  top.  This  was  aided  by  the  light 
from  a Ray  No.  90  Mogul  Projector,  furnished  with  a 125  Watt 
tungsten  bulb.  This  projector  was  located  12  inches  above  the 
chamber.  Under  this  condition  of  illumination^ a root  temperature 
of  25  C.  and  a shoot  temperature  of  30  C.  were  employed.  Pure 
silica  sand,  saturated  to  the  extent  of  20  per  cent,  served  as 
a medium,  and  a relative  humidity  of  30  per  cent  was  compared, 
in  its  effect  upon  growth,  with  a relative  humidity  of  90  per 
cent. 


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-26- 


Seedlings  growing  in  three  chambers  were  simultaneous- 
ly subjected  to  a given  set  of  the  environmental  conditions  al- 
ready named.  Since  each  chamber  accomodated  nine  seedlings, 

A 

the  data  on  growth,  under  a given  set  of  conditions,  were  obtain- 
ed from  27  seedlings  grown  in  separate  jars.  At  times,  however, 
some  of  the  individuals  exhibited  growth  rates  that  departed 
markedly  from  the  normal.  Askenasy  ('90),  True  ('95),  Lehen- 
bauer  ('14)  and  others  discarded  such  plants  and  based  their 
conclusions  on  the  data  gathered  from  those  individuals  ex- 
hibiting a normal  growth  rate.  This  procedure  appears  legitimate 
and  in  the  present  work  was  adopted.  In  such  cases^the  number 
of  individuals  for  a given  experiment  was  reduced.  In  no  case, 
however,  was  the  number  less  than  23. 

VI.  PRESENTATION  OF  DATA. 

Since  upwards  of  500  seedlings  were  studied  individually, 
it  is  evident  that  the  detailed  data  for  each  seedling  cannot 
be  given  in  a paper  of  this  length.  Even  if  it  were  possible 
to  present  all  of  the  figures,  it  seems  inadvisable  to  burden 
the  reader  with  a mass  of  detail,  especially  when  the  data  can 
be  condensed  and  presented  in  a form  that  will  show  at  a glance 
the  relative  values  of  different  treatments.  In  the  case  at 
hand^the  data  has  been  much  condensed,  but  the  aim  has  been  to 
present  as  much  as  is  necessary  for  a clear  and  correct  inter- 
pretation of  the  results. 


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-27- 


For  each  character  studied,,  the  mean  value  and  its 
probable  error  were  determined.  The  mean  weight  of  the  seeds 
was  determined  from  the  values  obtained  before  the  seeds  were 
placed  in  the  germinating  pan.  The  mean  weights  of  the  shoots, 
both  fresh  and  dry,  were  obtained  from  the  values  secured  at 
the  close  of  each  individual  experiment.  The  average  12-hour 
increment  of  elongation  for  each  individual  was  determined  from 
the  value  representing  the  total  increment  made  during  the  period 
of  observation.  From  these  12-hour  increments  the  means  were 
determined.  The  standard  deviations,  the  coefficients  of  variabil- 
ity and  their  probable  errors  were  obtained  in  the  usual  manner 
(Davanport,  *14). 

1.  Growth  of  Seedlings  in  Continuous  Darkness. 

In  Tables  I and  II  are  presented  the  data  showing 
the  rates  of  elongation  in  shoots  maintained  at  temperatures 
of  20°C.  and  30®C. , respectively.  From  inspection  of  the  data 
in  these  tables^it  may  be  observed  that  the  differences  in  the 
increments  of  elongation  between  the  seedlings  grown  under  any 
two  conditions  of  relative  humidity  indicated,  in  a soil  either 
20  per  cent  or  60  per  cent  saturated  with  water,  are  small. 
Comparing  the  seedlings  grown  in  either  soil  moisture, the  great- 
est difference  in  the  rate  of  elongation,  at  a temperature  of 
20*0.,  occurred  between  those  grown  in  a relative  humidity  of 
60  per  cent  and  those  grown  in  a relative  humidity  of  90  per 
cent.  With  a soil  20  per  cent  saturated, the  difference  in  the 


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-38- 


■ 

13-hour  increment  between  the  plants  referred  to  is  1.7-  .40; 
in  a soil  60  per  cent  saturated  the  difference  is  1.3^  .38. 

On  referring  to  a table  of  odds,  such  as  that  given  by  Wood 
(*11)  and  Davis  (*31),  it  may  be  found  that  the  odds  against 
such  differences  occurring  under  uniform  conditions  are  31  to 
1 and  9.5  to  1,  respectively.  At  a temperature  of  30® C.  these 
differences  are  less  significant  than  are  those  at  a temperature 
of  30®C. , as  the  greatest  difference  gives  odds  of  ^nly  3 to  1. 
Before  much  dependence  can  be  placed  an  a difference  being 
significant,  odds  of  at  least  30  to  1 are  demanded.  Therefore, 
in  the  oases  mentioned  above,  the  odds  are  not  sufficiently 
high  to  justify  the  placing  of  much  reliance  upon  the  seedlings, 
in  the  different  groups,  occupying  the  same  position,  relative- 
ly, if  the  experiments  were  repeated. 

Table  I.  Mean  13-hour  increments  of  elongation  in 

shoots  maintained  at  a temperature  of  30 ®C. 


Soil 

R.  humidity 

Mean 

Standard 

Coefficient  i 

moisture 

(per  cent) 

increment 

deviation 

variability 

(per  cent 
saturation) 
5 

30 

(in  mm. ) 
10. 8±  .35 

1.891  .18 

17. 5i  1.73 

60 

13. 5±  .19 

1.43±  .13 

11.5=  1.09 

90 

13. 3i  .33 

1.67±  .15 

13. 6±  1.37 

30 

30 

15. li  .19 

1.43±  .13 

9.4±  .86 

60 

14. 3±  .34 

1.86±  .17 

13. 1±  1.33 

90 

15. 9i  .33 

3.43^  .33 

15. 3±  1.48 

60 

30 

15. 0±  .17 

1.34±  .13 

9.0i  .83 

60 

14. 7±  .18 

1.37±  .13 

9.4i  .86 

90 

16. 0±  .33 

3.54±  .33 

15. 9±  1.49 

In  the  seedlings  grown  in  a sand  5 per  cent  saturated^ 
the  situation  is  somewhat  different.  The  differences  between 
the  mean  increments  of  the  seedlings  grown  in  a relative  humidity 


-V.'  iB'«‘dfesX«t'  «Ci*«r  -''ai  •■■  . 

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-29- 


of  30  per  cent  and  the  mean  increments  of  the  seedlings 
grown  in  a relative  humidity  of  60  per  cent,  at  temperatures 
of  20® C.  and  30°C.,  are  1.7±  .32  and  3.3i  .30,  respectively. 
Between  the  means  of  the  seedlings  grown  in  a relative  hmidity 
of  60  per  cent  and  the  means  of  the  seedlings  grown  in  a relative 
humidity  of  90  per  cent, the  differences  are  .8-  .29  and  .7*  .30. 
In  the  formerythe  differences  are  significant,  as  the  odds 
against  the  differences  being  due  to  pure  chance  are  over  110  to 
1 and  several  thousands  to  1,  respectively.  In  the  latter  j 
the  differences  are  not  significant,  as  the  odds  are  less  than 
5 to  1. 

Table  II.  Mean  12-hour  increments  of  elongation  in 

shoots  maintained  at  a temperature  of 
30®C. 

Soil  R.  humidity  Mean  Standard  Coefficient  of 

moisture  (per  cent)  increment  deviation  variability 

(per  cent  (in  mm. ) 

saturation) 


5 

30 

13. 0± 

.19 

1.44± 

.13 

11. 1± 

1.02 

60 

16. 3i 

.23 

1.80± 

.16 

11.  oj 

1.01 

90 

17.  Oi 

.19 

1.38± 

.13 

8.li 

.77 

20 

30 

19. 9± 

.20 

1.54± 

.14 

7.7± 

.71 

60 

20. 3i 

.28 

2.14± 

.20 

10. 5i 

.96 

90 

20.  Oi 

.32 

2.33± 

.23 

11. 6i 

1.14 

60 

30 

21. 3^ 

.42 

3.17i 

.30 

14. 9± 

1.58 

60 

21. 3i 

.23 

1.78^ 

.16 

8.4± 

.77 

90 

20.  li 

.39 

2.77i 

.28 

13. 5± 

1.37 

A fact  worthy  of  note  in  Tables  I and  II  is  that  of 
the  existence  of  a difference  in  the  rate  of  growth  between 
seedlings  grown  in  soils  of  different  water  content.  It  may 
be  observed  that,  at  the  three  relative  humidiljes  employed  and 

A 


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-30- 


at  both  temperatures,  the  differences  in  the  rate  of  growth 
between  the  seedlings  grown  in  a sand  20  per  cent  saturated 
and  the  seedlings  grown  in  a sand  60  per  cent  saturated  are 
small  and  without  significance.  Between  the  seedlings  grown 
in  a sand  5 per  cent  saturated  and  the  seedlings  grown  in  a 
sand  20  per  cent  saturated,  however,  marked  differences  are 
observable.  In  a relative  humidity  of  30  per  cent,, these 
differences  are  4.3-  .32  and  6.9i  .28;  in  a relative  humidity 
of  60  per  cent, l.?i  .30  and  4.0*  .36;  and  in  a relative  humidity 
of  90  per  cent, 2. 6*  .39  and  3.0*  .37.  Referring  to  Wood’s 
table  of  odds  it  may  be  found  that  the  odds  against  such  differ- 
ences being  due  to  chance,  sure  in  every  case,  upwards  of  125 
to  1 and  in  some  oases  reach  many  thousands  to  1.  Since  the 
odds  are  well  above  30  to  Ijit  is  evident  that  these  differences 
are  sufficiently  great  to  insure  that  relative  humidity  does 
exert  an  influence  upon  the  rate  of  shoot  elongation  in  seed- 
lings growing  in  sand  low  in  water  content. 

In  respect  to  rate  of  elongation, the  standard  deviar- 
tions,  Sts  given  in  Tables  I and  II,  are  only  in  certain  cases 
good  indices  of  variability.  Since  the  value  representing  the 
coefficient  of  variability  is  dependent  upon  the  relation  be- 
tween the  mean  increment  and  its  standard  deviation,  the  coeffi- 
cient of  variability  expresses  more  accurately  the  range  of 
variation.  Table  I brings  out  the  fact  that  at  a temperature 
of  20® C.  the  seedlings  grown  under  the  two  extreme  conditions. 


» > 


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1. ' 7. Hi?  151^  ¥,'3 


-31- 


in  respect  to  moisture,  possessed  the  greatest  degree  of 
variability.  At  a temperature  of  30® C.^ the  greatest  degree 
of  variability  was  exhibited  by  seedlings  grown  in  a sand  60 
per  cent  saturated. 

Tables  III  and  IV  furnish  the  data  supplying  the 
mean  fresh  weights  of  the  shoots  of  seedlings  grown  in  tempera- 
tures of  20®C.  and  30®C. , respectively.  The  values  indicate 
that,  at  both  temperatures,  there  existed  a close  relation  be- 
tween the  rates  of  elongation  and  the  fresh  weights  of  the 
shoots.  The  amount  of  water  in  the  sand  influenced,  to  a 
marked  degree,  the  amount  of  material  produced.  These  increases 
are  the  most  striking  in  the  rise  from  a soil  moisture  of  5 
per  cent  saturation  to  one  of  20  per  cent  saturation.  Beginning 
with  a relative  humidity  of  30  per  cent  and  ending  with  a 
relative  humidity  of  90  per  cent^the  increases  at  a temperature 
of  20®C.  are  .50-  .08,  .36^  .07  and  .81-  .05,  These  differences 
are  very  significant,  as  in  every  case  the  odds  sigainst  such 
differences  being  due  to  pure  chance  are  upwards  of  100  to  1. 

At  a temperature  of  30®C.,  the  increases,  in  the  same  order,  are 
.64f  .066,  .28^  .067  and  .27^  .066.  In  the  first  case^the 
chances  that  the  seedlings  in  this  group  would  occupy  the  same 
position,  relatively,  were  the  experiment  repeated,  are  several 
thousands  to  1;  in  the  second  case  about  21  to  1;  and  in  the 
third  case  about  20  to  1.  Since  the  odds,  in  the  last  two,  are 
below  thosg^enerally  accepted  as  the  minimum  for  certainty, 
the  significance  of  the  differences  are  open  to  question. 


I ill 


»«»  « 


-33- 


In  the  rise  from  a soil  moisture  of  20  per  cent  saturation  to 
one  of  60  per  cent  saturation, the  differences  at  both  ten5)era^ 
tures,  are  too  small  to  be  significant. 


Table  III.  Mean  fresh  weights  of  shoots  grown  in  an 

atmospheric  temperature  of  20°C. 


Soil 

moisture 
(per  cent 
saturation) 
5 


20 


60 


R.  humiditv 
(per  cent) 


Mean  weight 
(in  centi- 
grams) 


Standard  Coefficient  of 
deviation  variability 


30 

1.90i 

.05 

.41± 

.04 

21. 3± 

2.11 

60 

2.04± 

.03 

.26i 

.02 

12.6* 

1.20 

90 

2.13i 

.05 

.38± 

.03 

17. 6i 

1180 

30 

2.40± 

.06 

.45i 

.04 

18.5* 

1.75 

60 

2.40t 

.06 

.45i 

.04 

18.6* 

1.76 

90 

2.94± 

.07 

.54* 

.05 

18.7* 

1.82 

30 

2.62± 

.05 

.40^ 

.04 

15.1* 

1.41 

60 

2.67± 

.07 

.54* 

.05 

20.2* 

1.92 

90 

3.16± 

.09 

.67t 

.06 

21.2* 

2.02 

Table  IV.  Mean  fresh  weights  of  shoots  grown  in  an 
atmospheric  temperature  of  30® C. 


Soil 

R.  humidity 

Mean  weight 

Standard  - Coefficient  of 

moisture 

(per 

cent) 

(in  centi- 

deviation 

variability 

(per  cent 

grams) 

saturation) 

5 

30 

1.84*  .043 

.33* 

.030 

17. 9i  1.70 

60 

2.11*  .045 

.35* 

.032 

16.6*  1.56 

90 

2.23*  .043 

.32* 

.031 

14.3*  1.39 

20 

30 

2.48*  .05 

.39* 

.036 

15.7*  1.^47 

60 

2.39*  .05 

.39* 

.036 

16.3*  1.54 

90 

2.50*  .05 

.37* 

.036 

14.8*  1.47 

60 

30 

2.47*  .05 

.36* 

.034 

14.6*  1.40 

60 

2.57*  .05 

.37* 

.034 

14.4*  1.35 

90 

2.70*  .07 

.48* 

.048 

17.8*  1.82 

In 

Tables 

V and 

VI  are  presented  the 

mean 

values  of 

the  dry  weights  of  the  shoots  grown  under  the  various  conditions 
employed.  If  the  data  in  Table  V are  examined, it  may  be  found 


-33- 


that  the  differences  between  the  means  for  the  shoots  in  any 
two  groups,  grown  under  the  same  conditions  of  soil  moisture, 
are  insignificant.  With  but  two  exceptions  are  the  differences 
less  than  their  probable  errors.  At  a temperature  of  30° C. 
and  in  a soil  5 per  cent  saturated,  a relative  humidity  of  90 
per  cent  has  given  a much  greater  dry  weight  than  has  a relative 
humidity  of  30  per  cent.  In  this  case^ the  difference  is  3.4+  .54. 
This  gives  odds  of  upwards  of  30  to  1.  In  the  same  soil  water 
content, the  seedlings  grown  in  a relative  humidity  of  60  per 
cent  exhibited  a greater  dry  weight  than  did  those  grown  in  a 
relative  humidity  of  30  per  cent,  but  the  difference  is  not 
great  enough  to  rely  on  it  occupying  the  same  position,  relative- 
ly, were  the  experiments  repeated. 

It  may  be  observed  that  as  the  amount  of  soil  water 
increases  the  dry  weight  of  the  shoot  increases.  The  only  marked 
differences,  occurring  at  a temperature  of  20° C. , are  found  in 
passing  from  the  seedlings  grown  in  a soil  5 per  cent  saturated 
to  those  grown  in  a soil  20  per  cent  saturated.  Even  there  the 
differences  are  too  small  to  be  of  much  significance.  A signifi- 
cant increase  in  dry  weight,  brought  about  by  an  increase  in 
soil  moisture,  is  perceptible  in  the  seedlings  grown  in  a relative 
humidity  of  30  per  cent.  When  such  seedlings  grown  in  a soil 
5 per  cent  saturated,  are  compared  with  those  grown  in  a soil 
60  per  cent  saturated,  a difference  of  2.6i  .54  may  be  observed. 
This  value  furnishes  odds  of  about  50  to  1 that  the  difference 
is  due  to  environment  and  not  to  pure  chance.  At  a temperature 


-34- 


of  30®C.,the  only  significant  difference  (increase)  in  dry 
weight,  brought  about  by  an  increase  in  the  soil  water,  occurred 
also  in  seedlings  grown  in  a relative  humidity  of  30  per  cent. 

In  this  relative  humidity, the  means  of  the  seedlings  grown  in 
a sand  20  per  cent  saturated  exceeded  the  means  of  the  seedlings 
grown  in  a sand  5 per  cent  saturated  by  2.9-  .55.  This  differ- 

Table  V.  Mean  dry  weights  of  shoots  grown  in  an 
atmospheric  temperature  of  20  C. 


Soil 

R.  humidity  Mean  wt. 

Standard 

Coefficient 

Per  cent 

moisture 
(per  cent 
saturation) 

(per 

cent)  (in  eg.) 

deviat ion 

of  variabil- 
ity 

of  green 
wt . 

5 

30 

14. Oi  .43 

3.22± 

.31 

23.0= 

2.30 

7.3 

60 

14. 9±  .30 

2.29± 

.21 

15.41 

1.47 

7.3 

90 

15. 4i  .46 

3.3lt 

.32 

21. 5i 

2.22 

7.2 

20 

30 

16. Oi  .56 

4.21± 

.40 

26.31 

2.55 

6.7 

60 

15. 7±  .45 

3.50± 

.32 

22.3= 

2.15 

6.6 

90 

16. 4±  .32 

2.37± 

.23 

14.61 

1.42 

5.6 

60 

30 

16. 6±  .32 

2.43± 

.22 

14. 6± 

1.37 

6.3 

60 

17, Ot  .49 

3.781 

.35 

22. 2± 

2.27 

6.3 

90 

16.61  .42 

3.26i 

.30 

19.61 

1.87 

5.3 

ence,  according  to  Wood,  furnishes  odds  of  about  100  to  1 that 
a similar  difference  would  occur  again  under  the  same  conditions 
of  experimentation. 

On  further  examination  of  Tables  V and  VI, it  may  be 
observed  that  a constant  relation  between  the  mean  fresh  weights 
and  the  mean  dry  weights  of  the  shoots  of  seedlings,  subjected 
to  different  environmental  conditions,  does  not  exist.  As  the 
percentage  of  soil  moisture  was  increased, the  water  content  of 
the  resulting  shoots  became  higher.  This  appears  to  be  constant 
under  the  prevailing  experimental  conditions.  A fact  worthy 


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-35- 


of  note  in  this  connection  is  the  occurring  of  a difference 
in  the  part  played  by  the  soil  water  and  atmospheric  moisture 
at  the  two  temperatures  employed.  At  a temperature  of  20°C., 
relative  humidity  exerted  no  influence  on  the  per  cent- of  dry 
matter  present  in  the  shoots  of  seedlings  growing  in  a sand  5 
per  cent  saturated.  At  a temperature  of  30® C.,  with  the  same 
per  cent- of  soil  water,  this  did  not  hold.  In  seedlings  grown 
at  a temperature  of  20® C.  and  in  soil  moistures  of  20  per  cent 
and  60  per  cent  saturation,  relative  humidity  influenced,  to  a 
marked  degree,  the  per  cent  of  dry  matter  present;  while  in 
seedlings  grown  at  a temperature  of  30® C.  and  in  the  same  soil 
moistures,  differences  in  the  relative  humidity  brought  about 
only  slight  changes  in  the  per  cent  of  dry  matter  present. 


Table  VI.  Mean  dry  weights  of  shoots  grown  in  an 

atmospheric  temperature  of  30®C. 


Soil 

R.  humidity 

Mean 

wt . 

Standard 

Coefficient 

Per  cent 

moisture 
(per  cent 
saturation) 

(per  cent) 

(in  eg.) 

deviation  of  variabil- 
ity 

of  green 
wt . 

5 

30 

14.9* 

.41 

3.2* 

.29 

21.5- 

2.07 

8.1 

60 

16. 

.38 

2.9± 

.27 

17.6* 

1.67 

7.8 

90 

17. 3i 

.35 

2.6± 

.25 

15.0* 

1.46 

7.3 

20 

30 

17.8* 

.37 

2.9± 

.26 

16. 3± 

1.53 

7.2 

60 

17. 4± 

.43 

3.2i 

.29 

18.4* 

1.74 

7.3 

90 

16. 7± 

.41 

3.0* 

.39 

18.0* 

1.80 

6.7 

60 

30 

16. 9i 

.34 

2.6* 

.34 

15.4* 

1.53 

6.9 

60 

17.3* 

.32 

2.5* 

.23 

14.4* 

1.35 

6.7 

90 

18.0- 

.54 

3.8* 

.37 

21.1* 

2.18 

6.7 

Tables  VII  and  VIII 

bring  out 

the  relative  values  of 

different  combinations  of  soil  moistures  and  relative  hiimidities 


in  the  production  of  dry  weight  in  roots  of  seedlings.  In  the 


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-36- 


seedlings  grown  at  a temperature  of  20®C. , a condition  opposite 
to  that  occurring  in  shoots  may  be  observed.  In  roots  the 
greatest  dry  weights  occurred  in  seedlings  grown  in  a soil 
5 per  cent  saturated  and  in  a relative  humidity  of  30  per  cent, 
while  in  shoots  the  lowest  dry  weight  occurred  under  these  same 
conditions.  The  only  consistent  differences  in  the  mean  dry 
weights  in  the  roots  of  seedlings,  grown  at  this  temperature 
and  grown  under  the  same  conditions  of  soil  moisture,  occurred 
where  a soil  5 per  cent  saturated  was  employed.  But  even  there, 
the  value  by  which  the  seedlings  grown  in  the  lowest  relative 
humidity  exceed  the  seedlings  grown  in  the  highest  relative 
humidity  gives  odds  against  the  difference  being  due  to  chance 
of  less  than  20  to  1.  In  the  seedlings  grown  at  an  atmospheric 
temperature  of  30® C., the  maximum  dry  weight  occurred  under  con- 
ditions of  medium  soil  moisture.  The  differences  in  either  di- 
rection are  too  small  to  be  of  much  significance. 

Table  VII.  Mean  dry  weights  of  roots  of  seedlings  the 

shoots  of  which  were  maintained  at  a 
temperature  of  20*^0. 

Soil  R.  humidity  Mean  wt.  Standard  Coefficient  of 

moisture  (per  cent)  (in  eg.)  deviation  variability 
(per  cent 
saturation) 

5 


20 


60 


30 

4.7± 

.15 

1.09± 

.10 

23. 

,2± 

2.32 

60 

4.4± 

.10 

.72t 

.07 

16. 

,4t 

1.58 

90 

3.9± 

.13 

.92± 

.09 

23, 

,6± 

2.40 

30 

4.3i 

.12 

.95t 

.09 

22, 

.It 

2.13 

60 

4.0± 

.11 

.96± 

.08 

24. 

,0i 

2.33 

90 

4.2± 

.12 

.89± 

.08 

21, 

,2t 

2.11 

30 

4.oi 

.09 

.71± 

.06 

17. 

,7± 

1.68 

60 

4. it 

.12 

.97± 

.09 

23. 

2.28 

90 

3.8± 

.09 

.71± 

.06 

18. 

.7t 

1.76 

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-37- 


Table  VIII.  Mean  dry  weights  of  roots  of  seedlings, 

the  shoots  of  which  were  maintained 
at  a temperature  of  30° C. 


Soil 

R.  humidity 

Mean 

wt . 

Standard 

Coefficient  of 

moisture 

(per  cent) 

(in  ( 

) 

deviation 

variability 

(per  cent 
saturation) 
5 

30 

3.9i 

.14 

1.10±  .10 

28. 2± 

2.78 

60 

3.8l 

.10 

.74±  .07 

19. 5i 

1.85 

90 

4.2± 

.05 

.36^  .03 

8.6± 

.83 

20 

30 

4.2t 

4.1* 

.11 

.83±  .08 

19. 8i 

1.88 

60 

.08 

.63±  .06 

15. 4t 

1.45 

90 

4.2± 

.07 

.49±  .05 

11.71 

1.16 

60 

30 

3.9t 

.07 

.54±  .05 

13. 8± 

1.32 

60 

3.6j 

.06 

.45±  .04 

12. 5J 

1.17 

90 

3.7* 

.10 

.71±  .07 

19.2* 

1.97 

Table  IX.  Mean  weights  of  seeds  from  which  the  seed- 
lings grown  at  20°C.  were  obtained. 


Soil 

R.  humidity 

Mean 

wt. 

Standard 

Coefficient 

moisture 

(per  cent) 

(in  ( 

3g.  ) 

deviation 

variability 

(per  cent 
saturation) 
5 

30 

44.  Oi 

1.09 

8.09i  .77 

18. 3± 

1.80 

60 

43. 0± 

. 66 

5.07±  .47 

11,  et 

1.13 

90 

46. 0± 

1.01 

7.77±  .71 

16. 9± 

1.73 

20 

30 

47. 6± 

.97 

7.30±  .68 

15. 3± 

1.47 

60 

46. 7± 

1.07 

8.25±  .76 

17. 7t 

1.67 

90 

47.  Oi 

.70 

5.20i  .49 

11. 1± 

1.08 

60 

30 

44. 3± 

.78 

6.03*^  .55 

13. 6± 

1.27 

60 

47.  Oi 

1102 

7.82±  .72 

16. 6i 

1.55 

90 

46.6- 

.94 

7.61±  .66 

16. 3± 

1.53 

On  examination  of  Tables  IX  and  X it  may  be  observed 
that  the  differences  occurring  between  any  two  means  in  seed 
weights  are  small.  The  greatest  differences  in  mean  weights  of 
seeds,  from  which  the  seedlings  grown  under  the  different  en- 
vironments were  obtained,  amounts  to  7~  1.6  and  1.3.  In  both 
cases  the  differences  give  odds  of  less  than  25  to  1.  Since 


-38- 


these  odds  are  rather  small  to  be  significant,  the  differences 
in  the  rates  of  elongation  cannot  be  accounted  for  through  differ- 
ences in  the  weights  of  the  seeds  employed. 

Table  X.  Mean  weights  of  seeds  from  which  the  seed- 


lings 

grown  at 

• 

0 

0 

0 

to 

' were 

obtained 

Soil 

R.  humidity 

Mean 

wt . 

Standard 

Coefficient  ( 

moisture 
(per  cent 
saturation) 

(per  cent) 

(in  eg.) 

deviation 

9^ 

L variability 

5 

30 

42-  1. 

3 

9.71 

.90 

23.11 

2.22 

60 

45±  . 

96 

7.4I 

.68 

16. 4± 

1.55 

90 

471  . 

69 

5.3l 

,49 

11. 3I 

1.09 

20 

30 

491  . 

96 

7.4i 

.68 

15.1- 

1.42 

60 

46i  . 

96 

7.41 

.68 

16.  li 

1.52 

90 

45l  . 

84 

6.ll 

.69 

13. 6± 

1.34 

60 

30 

45-  . 

78 

5.91 

.55 

13.  ll 

1.25 

60 

44±  . 

83 

6.4I 

.59 

14.51 

1.36 

90 

47l  1. 

21 

8.6l 

.85 

18.21 

1.87 

Tables  XI  and  XII  furnish  the  mean  total  increments 
of  elongation  in  the  shoots  of  seedlings  grown  under  the  differ- 
ent conditions  of  temperature,  soil  moisture  and  relative  humid- 
ity employed.  On  examination  of  the  tables  it  may  be  found 
that,  with  but  one  exception,  the  seedlings  grown  in  a soil 
moisture  of  5 per  cent  saturation  made  smaller  total  increments 
than  those  grown  in  the  higher  soil  moistures.  The  differences 
in  every  case,  excepting  the  one  referred  to,  are  significant. 
Between  the  seedlings  grown  in  a soil  moisture  of  20  per  cent 
and  those  grown  in  a soil  moisture  of  60  per  cent  saturation j 
the  only  significant  differences  may  be  found  in  t^liose 
grown  at  a temperature  of  20  C.  and  in  a relative  humidity  of 
60  per  cent.  In  this  instance^ the  difference  is  59^  6.76. 


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-39- 


Differences  brought  about  by  relative  humidity  occur  in  a few 
cases.  In  Table  Xl,  it  may  be  observed  that  in  a soil  moisture 
of  20  per  cent  saturation  the  seedlings  grown  in  a relative 
humidity  of  60  per  cent  made  an  increment  significantly  smaller 
than  those  grown  in  relative  humidities  of  either  30  per  cent 

or  90  per  cent.  In  the  same  table,  but  in  a soil  60  per  cent 

saturatid^the  seedlings  grown  in  a relative  humidity  of  60  per 
cent  exceeded  those  grown  in  a relative  humidity  of  30  per  cent 
by  42^  7.82.  In  this  case^the  odds  that  the  difference  is  not 
due  to  pure  chance  are  about  100  to  1.  In  Table  XII  a signifi- 
cant increase  brought  about  by  an  increase  in  the  relative  humid- 
ity may  be  found  in  the  seedlings  grown  in  a soil  moisture  of  5 

per  cent  saturation.  The  difference  referred  to  occurs  between 
those  grown  in  relative  humidities  of  30  per  cent  and  60  per  cent ^ 

Table  XI.  Mean  total  increments  of  elongation  in  shoots 
maintained  at  a temperature  of  20® C. 


Soil  R 

. humiditv 

Mean 

incre- 

Standard  Coefficient  of 

moisture 

(per  cent) 

ment 

(in  mm. ) 

deviation  variability 

(per  cent 
saturation) 
5 

30 

2471 

2.70 

20. 0l 

1.91 

8.li 

.77 

60 

262- 

3.40 

25. 7± 

2.40 

9.8± 

.92 

90 

2311 

6.96 

53.61 

4.93 

23.21 

2.42 

20 

30 

3011 

4.39 

33.21 

3.12 

11.  ol 

1.03 

60 

2571 

5.61 

43.11 

3.96 

16.81 

1.58 

90 

3081 

5.61 

41.61 

3.96 

13.51 

1.31 

60 

30 

2741 

6.85 

52.71 

4.85 

19. 2± 

1.83 

60 

3161 

3.78 

29.  ll 

2. 66 

9.2l 

.84 

90 

306* 

5.50 

42.31 

3.89 

13. 8± 

1.29 

respectively. 

The  odds 

in  this  case, 

according  to 

Wood  ( 

'll), 

approach  1000  to  1. 


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-40- 


Table  XII.  Mean  total  increments  of  elongation  in 

shoots  maintained  in  a temperature  of 
2>0^C. 


Soil 

R.  humidity 

Mean 

incre- 

Standard 

Coefficient  of 

moisture  (per  cent) 

(per  cent 
saturation) 

ment 

(in  mm. ) 

deviation 

variability 

5 

30 

3331 

4.28 

32. 9±  3.02 

14.1*  1.32 

60 

2741 

4.40 

33. 8^  3.10 

13. 3I  1.15 

90 

2561 

3.68 

27. 3t  2.60 

10.7*  1.04 

20 

30 

3151 

3.55 

27. 4I  2.51 

8.7*  .79 

60 

3061 

4.13 

31.81  2.92 

10.4*  .96 

90 

2881 

6.22 

45. 2I  4.40 

15.71  1.56 

60 

30 

320l 

3.88 

29. 3t  2.74 

9.1*  .85 

60 

3001 

3.92 

30. 2t  2.77 

10. ll  .93 
10.61  1.06 

90 

3141 

4.70 

33.4*  3.32 

Mention  may  here  be 

made  of  the  general  ( 

sharacter  of 

the  root 

systems  found  - 

on  the 

seedlings 

grown  in  silica  sand  of 

different  moisture  contents.  No  actual  dataare  available,  but 


striking  differences  in  the  length  and  the  extent  of  the  branch- 
ing in  the  root  systems  were  observed.  Seedlings  grown  in  a 
sand  5 per  cent  saturated  possessed  a short  main  root  with  many 
laterals.  Those  grown  in  a sand  60  per  cent  saturated  possessed 
a long  main  root  with  few  laterals.  Those  grown  in  a sand  20 
per  cent  saturated  possessed  roots  occupying  a position,  in 
respect  to  character,  intermediate  between  the  other  two.  In 
the  seedlings  of  the  last  group^the  main  roots  were  moderately 
long  and  the  lateral  roots  more  numerous  than  in  those  grown 
in  a sand  60  per  cent  saturated. 

3..  Growth  of  Seedlings  in  Darkness  Alternating 

with  Light. 

The  data  presented  in  Tables  XIII  and  XIV  give  the 


-41- 


inorernents  of  elongation  and  the  total  fresh  weights  in  bean 
seedlings  that  were  subjected  to  a daily  illumination  of  12  hours. 
On  inspection  of  the  data  it  may  be  found  that  the  mean  12-hour 
increments  are  the  same.  In  respect  to  fresh  weight,  the  value 
for  the  seedlings  grown  in  a relative  humidity  of  90  per  cent  is 
the  higher,  but  it  exceeds  the  value  for  the  seedlings  grown  in 
a relative  humidity  of  30  per  cent  by  only  .09-  .063.  It  is 
evident  that  this  difference  is  too  small  to  be  significant. 

From  the  data  presented  in  these  tables  it  appears  that,  under 
the  conditions  of  the  experiment  in  question,  a low  relative 
humidity  is  as  favorable  as  a high  relative  humidity  in  the 
formation  of  fresh  material  in  shoots  of  bean  seedlings. 

Table  XIII.  Mean  13-hour  increments  of  elongation  in 

shoots  maintained  in  a temperature  of 
30°  C. 

Soil  R.  humidity  Mean  incre-  Standard  Coefficient  of 

moisture  (per  cent)  ments  (in  mm.)  deviation  variability 
(per  cent 
saturation) 

20  30  17,21:  .19  1.44t  .13  8.4±  .77 

90  17. 2t  .29  2.14t  .20  12.4±1.20 


Table  XIV.  Mean  fresh  weight  of  shoots  maintained  in 

a temperature  of  30° C. 

Soil  R.  humidity  Mean  weights  Standard  Coefficient  of 

meisture  (per  cant)  (in  grams)  deviation  variability 
(per  cent 
saturation) 

30  30  2.15t  .041  .32t  .039  14.91:  1.40 

90  2.24i  .050  .37±  .035  16.61  1;02 

On  comparing  the  values  in  these  tables  with  the 

corresponding  values  for  the  seedlings  grown  in  continuous 

darkness,  significant  differences  are  found.  In  the  rate  of 


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-42- 


elongation,  the  seedlings  grown  in  continuous  darkness  exceeded 

those  grown  in  part  time  illumination  by  values  that  give  odds 

not 

of  upwards  of  1000  to  1 that  the  differences  are^due  to  pure 
chance.  In  respect  to  fresh  weight,  the  only  difference  giving 
odds  above  30  to  1 occurs  in  the  seedlings  grown  in  a relative 
humidity  of  30  per  cent. 

Table  XV.  Mean  total  increments  of  elongation  in 

shoots  maintained  in  a temperature  of 
30®C. 

Soil  R.  humidity  Mean  incre-  Standard  Coefficient  of 

moisture  (per  cent)  ment  (in  mm.)  deviation  variability 

(per  cent 
saturation) 

20  30  2191  2.41  18. 5^  1.70  8.4t  .77 

90  241^  3.50  25. 9±  2.48  10. 7±  1.03 

In  Table  XV  the  difference  in  the  mean  total  increments 
of  elongation  in  the  illuminated  shoots  is  shown.  The  differ- 
ence occurring  is  22^  4.25.  Considering  the  probable  error, 
this  furnishes  odds  of  about  75  to  1 that  the  difference  is  not 
due  to  pure  chance.  Since  these  odds  are  above  the  minimum 
accepted  for  certainty,  this  difference  may  be  considered  signi- 
ficant. 

The  total  increments  of  elongation,  as  given  in  Table 
XV,  are  decidedly  smaller  than  the  corresponding  ones  in  Table 
XII.  In  the  two  relative  humidities  (30  per  cent  and  90  per  cent) 
the  differences  occurring  are  100-  4.23  and  47i  7.14,  respective- 
ly. In  the  former  case, the  odds  that  the  difference  is  not  due 
to  chance  are  upwards  of  1,000,000  to  1;  in  the  latter  casej up- 
wards of  500  to  1.  These  odds  are  sufficiently  great  to  be  sig- 
nificant. 


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-43- 


Table  XVI  brings  out  the  difference  in  the  dry  weight 
of  shoots  subjected  to  relative  humidities  of  30  per  cent  and 
90  per  cent,  respectively.  The  difference  occurring  is  3.0-  .70. 

While  this  difference  appears  great  enough  to  be  significant^ 
odds  of  only  22  to  1,  that  each  would  occupy  the  same  relative 
position  upon  repeating  the  experiment,  are  found  when  due  con- 
sideration is  given  the  probable  error.  If  we  are  to  accept 
odds  of  30  to  1 as  our  measure  of  certainty^ little  reliance  can 
be  placed  on  the  above  difference  being  due  to  a difference  in 
the  relative  humidity.  It  may  be  observed  that  a wide  differ- 
ence occurs  between  the  values  representing  the  degree  of  varia- 
bility. The  difference,  though  14. 6t  3.72,  is  too  small  to  be 
significant,  as  the  odds  are  less  than  20  to  1.  On  further  ex- 
amination of  the  table^  a difference  in  the  per  cent  of  dry 
material  produced,  in  the  respective  relative  hiimidities,  may 
be  observed.  While  similar  to  that  occurring  in  the  etiolated 
seedlings  this  difference  is  much  more  striking. 

Table  XVI.  Mean  dry  weights  of  shoots  grown  in  an 

atmospheric  temperature  of  30® C. 

Soil  R.  humidity  Mean  wt.  Standard  Coefficient  Per  cent 

moisture  (percent)  (in  eg.)  deviation  of  varia^  of  green 
(per  cent  bility  wt. 

saturation) 

20  30  16. 8±  .38  2.9±  .27  17, 3^  1.64  7.8 

90  13. 8i  .59  4.4t  .42  31. 9±  3.34  6.2 

The  difference  between  the  dry  weights  in  roots  of 
seedlings,  as  brought  out  in  Table  XVII,  is  not  striking.  Al- 
though the  difference  is  .3-  .13,  the  probable  error  is  of  such 


-44- 

magnitude  that  but  little  reliance  can  be  placed  upon  their 
holding  the  same  position, if  the  experiment  were  repeated.  It 
may  be  observed,  however,  although  the  differences  are  not  great 
enough  to  be  significant,  that  the  relation  of  shoot  and  root 
to  moisture  supply  appear  to  be  the  same  in  the  seedlings  grown 
in  part  time  illumination  as  in  the  seedlings  grown  in  continuous 
darkness. 


Table  XVII.  Mean  dry  weights  of  roots  of  seedlings 

the  shoots  of  which  were  maintained 
in  a temperature  of  30° C. 


Soil  R.  humidity 

moisture  (per  cent) 

(per  cent 
saturation) 

20  30 

90 


Mean  weight  Standard  Coefficient  of 

(in  eg.)  deviation  variability 

4.2±  .088  .68^  .062  16. 2±  1.54 

3.9±  .084  .62i  .059  15. 9^  1.55 


As  in  the  case  of  the  etiolated  seedlings,  the  differ- 
ence between  the  mean  weights  of  the  seeds,  from  which  the  two 
groups  of  illuminated  seedlings  were  grown,  is  small.  The  differ- 
ence, as  indicated  in  Table  XVIII,  is  only  2^  1.27.  Little 
assurance  is  afforded  that  the  same  ofder  of  values  would  hold 
upon  repeating  the  experiment. 

Table  XVIII.  Mean  weights  of  seeds  from  which  the 

seedlings  grown  at  30  C.  were  obtained. 

Soil  R.  humidity  Mean  weight  Standard  Coefficient  of 

moisture  (per  cent)  (in  eg.)  deviation  variability 

(per  cent 
saturation) 

20  30  45±  .95  7.3±  .67  16. 2±  1.53 

90  43±  .85  6.3±  .60  14. 6t  1.42 

In  respect  to  mean  dry  weights  of  shoots,  mean  dry 
weights  of  roots  and  mean  weights  of  seeds,  significant  differ- 


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-45- 


ences  between  the  values  given  in  Tables  XVI,  XVII  and  XVIII 
and  the  corresponding  values  in  Tables  VI,  VIII  and  X do  not 
appear. 

The  seedlings  grown  in  darkness  alternating  with  light 
differed  in  their  characters  from  those  grown  in  continuous  dark- 
ness. One  of  the  chief  differences  occurred  in  leaf  development. 
The  leaves  of  the  seedlings  maintained  in  darkness  remained  small 
and  in  many  cases  did  not  unfold.  The  leaves  of  the  seedlings 
grown  in  darkness  alternated  with  light  unfolded  early,  and  at 
the  conclusion  of  the  experiment  had  attained  a size  several 
times  that  of  the  leaves  in  the  etiolated  seedlings.  Another 
important  difference  between  these  two  groups  of  seedlings  was 
in  color.  The  seedlings  grown  in  darkness  alternated  with  light 
developed  a deep  green  color,  while  those  grown  in  continuous 
darkness  remained  pale  yellow.  This  greening  in  the  seedlings 
illximinated  part  time  could  be  observed  soon  after  their  exposure 
to  light,  and  at  the  end  of  the  first  day  the  primary  leaves 

exhibited  the  color  characterizing  normal, illuminated  pllants. 

In  addition  to  the  data  presented  In  the  previous 
tables,  data  were  obtained  on  the  amounts  of  water  given  off 
by  the  seedlings  during  the  period  of  observation.  In  the 
present  paper  these  data  have  been  omitted,  owing  to  plans  to 
present  them  in  a separate  paper  in  the  near  future. 

The  results  of  our  experiments  briefly  summarized 
show:  (1)  that  only  in  a soil  5 per  cent  saturated  is  there  a 
significant  increase  in  the  rate  of  elongation  brought  about  by 


-46- 


an  increase  in  the  relative  humidity;  (2)  that  as  the  soil  water 
is  increased  from  5 per  cent  saturation  to  20  per  cent  saturation 
a significant  increase  in  the  rate  of  elongation  in  etiolated 
shoots  occurs;  (3)  that,  in  general,  the  higher  the  moisture 
supply,  either  in  the  atmosphere  or  in  the  soil,  the  lower  is 
the  per  cent  of  dry  matter  in  the  plant;  (4)  that  changes  in 
the  amount  of  soil  water  from  5 per  cent  to  60  per  cent  satura- 
tion do  not  bring  about  significant  changes  in  the  relation  be- 
tween the  dry  weights  of  root  and  shoot^  (5)  that  light  retards 
growth. 

VII.  DISCUSSION. 

Already,  attention  has  been  called  to  the  fact  that 
the  results  obtained  on  growth  in  relation  to  relative  humidity, 
in  this  investigation,  do  not  accord  with  the  results  obtained 
in  some  of  the  previous  investigations.  The  data  furnished  by 
these  other  investigators  do  not  allow  of  an  explanation  of  the 
discrepancies.  If  an  exact  knowledge  of  the  conditions  under 
which  these  investigators  worked  were  known^it  is  probable 
that  these  differences,  in  part  at  least,  could  be  accounted 
for.  It  is  true  that  plants  of  all  species  do  not  agree  in 
their  response  to  every  environmenteil  condition.  It  is  possible 
that  plants  of  one  species  may  react  more  favorably  to  a high 
relative  humidity  than  to  a low  one  and  that  plants  of  another 
species,  under  the  same  conditions  of  environment,  may  react 
more  favorably  to  a low  relative  humidity  than  to  a high  one. 


I-* 


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-47- 


A definite  answer  to  this  question,  however,  awaits  future  in- 
vestigation. Imperfect  control  of  the  environmental,  conditions 
in  the  previous  investigations  are  responsible,  in  a large 
measure,  for  the  differences  obtained.  In  some  oases  contribu- 
ting environmental  factors  have  been  entirely  overlooked  and 

were 

the  data  presented^obtained  from  plants  or  seedlings  grown  under 

from 

conditions  widely  different  ^ those  indicated. 

In  previous  researches  on  growth  in  relation  to  en- 
vironmental conditions,  with  but  few  exceptions  the  cultures 
under  observation  have  comprised  but  small  numbers  of  individuals. 
In  only  a few  cases  has  the  number  exceeded  ten  and  in  many 
cases  the  number  employed  has  been  less  than  five.  It  has  been 
pointed  out  by  recent  workers  that  conclusions  based  on  such 
small  samples  may  be  entirely  erroneous.  It  is  known  that 
plants  of  the  same  species,  under  the  same  conditions  of  environ- 
ment, show  wide  variations  in  the  rate  of  elongation.  The 
plants  or  seedlings  exhibiting  the  highest  growth  rate,  among 
those  in  an  unfavorable  environment,  may  make  more  rapid  growth 
than  the  plants  or  seedlings  exhibiting  the  lowest  growth  rate 
among  those  in  a favorable  environment.  If,  in  comparing  two 
environments  in  respect  to  their  effect  upon  growth,  the  plants 
selected  should  fall  in  the  classes  referred  to,  it  is  obvious 
that  the  conclusions  drawn  would  be  misleading.  Thus,  it  may 
be  seen  that  conclusions  drawn  from  few  individuals  or  from  few 
cultures  may  lead  to  grave  error.  Considering  the  great  com- 
plexity in  the  factors  conditioning  the  results,  and  the  absence 


-48- 


I 

of  full  appreciation  of  these,  lack  of  consistency  in  the  con- 
clusions reached  by  earlier  investigators  is  to  be  expected. 

The  results  of  Sorauer  ('80),  Reinitzer  ('81),  Reinke 
('76),  Wollny  (*98),  Anderson  ('94),  Darwin  ('93),  Clark  ('78), 
Tsclaplowitz  ('86)  and  Eberhardt  ('03)  apparently  agree,  only  in 
part,  with  the  results  obtained  in  the  present  investigation. 

While  some  of  these  investigators  secured  very  marked  advantages 
in  favor  of  the  higher  relative  humidities,  others  secured  only 
a slight  balance  in  that  direction.  A definite  explanation  for 
these  differences  in  growth  cannot  be  given.  It  has  been  stated 
already  that  there  is  a possibility  of  plants  of  different  species 
responding  differently  to  a given  set  of  conditions.  By  some 
it  may  be  suggested  that  the  great  diversity  of  plants  employed, 
in  the  experiments  referred  to,  will  account  for  the  discrepan- 
cies. There  is,  however,  no  experimental  evidence  to  lend 
support  to  such  a view.  The  small  differences  shown  in  the 
tables  presented  by  some  of  these  investigators  are  no  greater 
than  the  differences  which, in  this  discussion, have  been  con- 
sidered insignificant.  In  addition,  the  number  of  cultures 
employed  in  the  present  investigation  greatly  exceeds  the  number 
employed  in  any  of  the  investigations  referred  to.  In  fact,  in 
some  oases  the  conclusions  reached  by  former  investigators  were 
based  upon  the  growth  of  a single  individual.  'This  renders 
their  differences  less  significant  than  if  larger  numbers  had 
been  employed.  Owing  to  the  use  of  such  small  numbers,  it 

— ■ ■ — 


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-49- 


raay  be  that  the  differences  obtained  are  only  chance  differences 
and  that,  if  the  experiments  were  repeated,  the  lower  relative 
humidity  would  be  equally  as  favorable  to  growth  as  the  higher 
relative  humidity. 

On  the  other  hand, the  results  obtained  by  Schaible 
COl)  agree  with  the  results  obtained,  in  the  present  investiga- 
tion, on  seedlings  grown  in  a sand  high  in  water  content.  If 
Vesque  and  Viet  (’81)  had  based  their  conclusiohs  upon  the  average 
growth  of  all  individuals  grown,  rather  than  upon  the  best  individ- 
ual from  each  group,  their  conclusions  would  have  agreed  very 
well  with  those  of  Schaible. 

Since  the  dry  air  admitted  to  the  plant  chambers  was 
not  controlled,  in  the  investigations  mentioned,  it  is  not  un- 
likely that  in  some  cases  the  relative  humidity  reached  a value 
much  lower  than  the  lowest  employed  in  the  present  investigation. 
Where  very  marked  differences  in  the  growth  rate  between  seedlings 
grown  in  a dry  atmosphere  and  seedlings  grown  in  a moist  atmos- 
phere occurred,  as  in  the  investigations  of  Reinitzer  (’81),  the 
air  on  entering  the  plant  chamber  was  passed  through  tubes  con- 
taining pumice  stone  moistened  with  sulphuric  acid.  Under  such 
conditions,  the  relative  humidity  of  the  air  entering  the  plant 
chamber  undoubtedly  reached  a value  below  30  per  cent.  This 
very  low  relative  humidity,  possibly  combined  with  unfavorable 
conditions  of  soil  moisture,  may  assist  in  accounting  for  the 
wide  differences  in  the  growth  rates  recorded. 


5 fc;,.  -r''' 


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-50- 


The  data  presented  in  the  previous  section  of  this 
paper  bring  out  the  fact  that  in  a study  of  growth  in  relation 
to  relative  humidity  soil  moisture  must  be  considered.  In  these 
experiments,  a silica  sand  20  per  cent  saturated  has  proved  to 
be  capable  of  supplying  water  to  seedlings,  growing  in  a relative 
humidity  of  30  per  cent,  as  r^idly  as  required  for  maximum 
growth.  This  confirms  the  conclusions  reached  by  Hellriegel  ('83) 
who  recognized  that  the  amount  of  water  given  off  by  the  plant 
exerted  no  retarding  influence  upon  the  growth  rate,  so  long 
as  the  amount  of  water  in  the  soil  was  maintained  within  favor- 
able limits.  The  observation  of  Hellriegel  ('69),  Fittbogen 
(•73),  Sorauer  ('73),  Wollny  ('88,  '92,  *97),  Gain  ('92,  *95,  (96), 
Shroeder  ('96),  Mayer  ('98),  Tucker  and  Seelhorst  ('98),  Pagnoul 
('99),  Seelhorst  ('00),  Prianishnikov  ('00),  Seelhorst  and 
Freckmann  ('03),  Hunger  ('06),  Preul  ('08),  Harris  ('14),  Kies- 
selbaoh  ('15),  Shine  ('20)  and  others  are  not  at  variance  with 
this  view.  Although  the  above  investigators  make  no  mention  of 
relative  humidity  in  their  investigations,  evidence  is  presented 
in  favor  of  the  view  that  soil  moisture  is  a very  important 
factor  in  determining  growth  rate  in  plants.  Burkholder  ('19) 
has  shown  that  plants  of  the  common  bean,  affected  by  the  dry 
root- rot,  are  able  to  carry  on  their  normal  functions  if  an 
abundance  of  water  is  present  in  the  soil.  If,  however,  the 
soil  moisture  decreases,  the  few  remaining  roots  are  unable  to 
supply  the  plant  with  the  requisite  amount  of  water  and  the 
growth  rate  decreases  accordingly.  The  data  presented  in  this 


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-51- 


paper  show  that  in  a sand  only  5 per  cent  saturated  the  avail- 
able water  is  not  present  in  sufficient  amounts  to  supply  the 
needs  of  the  plant  for  maximum  growth.  Under  such  conditions 
of  soil  moisture,  a higher  growth  rate  would  be  expected  in  the 
presence  of  a high  relative  humidity  than  in  the  presence  of  a 
low  relative  humidity.  This  occurred  in  the  present  investiga- 
tion. From  these  considerations  it  seems  probable  that  soil 
moisture  was  a limiting  factor  (Blackman,  *05)  in  at  least  some 
of  the  investigations  referred  to. 

The  observations  of  Kraus  (*95),  Lock  (’04)  and  Smith 
(’06),  agree  with  those  of  Reinitzer  (’81),  Smith  (’06)  and 
Lock  (’04)  attributed  to  relative  humidity  a great  role 
in  determining  the  growth  rate  in  shoots  of  Dendro calamus.  This 
may  have  been  warranted,  but  the  data  on  growth  in  bean  seed- 
lings presented  in  this  paper  show  that  in  doing  so  soil  moisture 
must  receive  due  consideration.  The  evidence  brought  forth  in 
Table  I suggests  that  the  relation  between  relative  humidity 
and  plant  growth  is  more  complex  than  these  authors  have  in- 
dicated. This  complexity  in  the  environmental  relations  of 
plants  growing  in  nature  is  further  brought  out  by  the  observa- 
tions of  Douglas  (’06),  Greeley  (’20),  Maxwell  (’96),  Prantl 
(’73),  Stebler  (’78)  and  others. 

That  relative  humidity,  as  a factor  influencing  the 
growth  rate, has  been  greatly  overestimated  and  that  soil  mois- 
ture^ in  this  respect, has  been  greatly  underestimated  is  supported 


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-52- 


by  the  conclusions  reached  by  Shibata.  A curve  representing 
the  growth  rate  in  shoots  of  Dendrocalamus^ as  observed  by  him, 
shows  no  relation  to  the  corresponding  curve  for  relative  humid- 
ity. While  the  relative  humidity,  at  times,  reached  a low  value, 
the  water  required  was  present  in  the  soil  in  sufficient  amounts 
to  supply  the  needs  of  the  plants,  without  inducing  a depression 
in  the  growth  rate. 

The  relation  of  growth  rate  to  soil  moisture,  as  shown 
in  Tables  I and  II ^confirms  the  conclusions  reached  by  Pearson 
(’18),  Douglas  ('09,  ’14),  Kelsick  (’18),  Kirkwood  (’14),  Bogus 
(’05),  and  Taylor  and  Downing  (’17),  Pearson  states,  "The  im- 
portant fact  pointed  out  by  this  study,  however,  is  that  it  is 
the  April  and  May  precipitation  which  is  most  .important  in  deter- 
mining the  amount  of  height^growth  and  presumably  the  moisture 
content  of  the  soil  during  the  period  when  height  growth  takes 
place".  Similar  conclusions  were  reached  by  the  remaining 
authors. 

With  respect  to  the  effect  of  soil  moisture  upon  the 
weight  of  material  produced  in  root  and  in  shoot,  the  results 
given  in  Tables  III  - VIII  and  XV  - XVII  in  this  paper  agree 
only  in  part  with  those  of  Hellriegel  (’69),  Sorauer  (’73), 

Gain  (’92,  ’95,  ’96),  Shroeder  (’96),  Mayer  (’98),  Wollny  (’98), 
Tucker  and  Seelhorst  (’98),  Pagnoul  (’00),  Seelhorst  and  Freck- 
mann  (’03),  Bunger  (’06),  Preul  (’08),  Seelhorst  and  Kizymowski 
(’10)  and  Shive  (’20).  The  above  authors  seem  to  agree  in  hav- 
ing observed  that  from  an  increase  in  the  soil  moisture,  in- 
creases in  the  fresh  and  dry  weights  of  the  shoot  and  a decrease 


-53- 


in  the  dry  weight  of  the  root  result.  Tucker  and  Seelhorst 
(•98)  state  •’Die  Ausbildung  der  oberirdischen  Pflanzensubstanz 
der  Haferpflanze  nahm  mit  steigendem  Wassergehalt  zu;  bei  den 
Wurzeln  war  das  Umgek^rte  der  Fall.  Bei  einem  ger ingen  Wasser- 
gehalt des  Bodens  trat  die  relativ  gr6sste  Ausbildung  der  Wurz- 
eln die  relative  geringste  der  oberirdischen  Masse  ein”.  Their 
data'  indicate  increases  in  the  weight  of  plant  substance  with 
increases  in  the  soil  moisture,  until  the  soil  reaches  a point 
where  it  is  from  60  per  cent  to  90  per  cent  saturated.  Omitting 
the  probable  error,  the  data  furnished  lim  the  tables  referred 
to  confirm,  in  a general  way,  the  results  obtained  by  these 

authors.  However,  when  consideration  is  given  this  error,  these 
d 

data  ir^oate  no  significant  increases  in  the  weights  of  the 
plants,  beyond  a soil  moisture  of  30  per  cent  saturation.  It 
must  not  be  forgotten  that  in  the  investigations  already  referred 
to,  the  plants  were  grown  for  a longer  period  than  were  those 
in  the  present  investigation.  The  wide  difference  in  the  stage 
of  development  at  the  time  of  analysis  may  account  for  the  dis- 
crepancies noted.  The  absence  of  light  in  the  plant  chambers 
employed,  as  indicated,  and  differences  in  temperature  and  rela- 
tive humidity  may  be  important  factors  for  consideration  in  this 
connection.  A similar  explanation  to  that  of  the  former  may  be 
suggested  for  the  results  obtained  by  Polle  (’10)  on  seedlings 
of  wheat  and  barley,  which  agree  with  those  obtained  in  the 
present  investigation. 

With  respect  to  the  relation  between  fresh  and  dry 


Crt  iiA'  -!3 9’^’% * V i ii4  *^-  v c»fl  ■■  t ^ ; *. 


Q 


. r \ 


■'.^  .V. ',; ;, ■' -^  -A  .,  . r:KAi’  sfer , 

/.'  " ■ ■■  4 ' •■  “ r, ' " ' ses 

U ■'  "■  i,  it:!V'^cnil(ror.6i' , 

" , ■ * ' '•  ^ 'i*  / A_'^Vj  1”  ^ 'i ' ' '■"”  ' ^' ' 'ii 

‘ ''  '^<4!!^'*3^i' ■ ''■  ’ , ' 4 '.  *'  '•  /*■«' i 4 ■ j ' iW^  I ‘‘  _€  bl  ’.*^.  ' ,i‘,' 


' : . ,■ 


P’  I /'■*••»  ','  V . ■/  y "^'"'  ]j*  ^ * -■  "-"“  ya^  ,«^  ^ 

:'r  '•>>'•■  '■  _ , .cropfeetfl 


m ' ' ' ','v®,;'  . 'V.  ■■ 


,-  ~44it4.  ■^Tiitik  •■^'  ...  Jli;  ' •>  '^  . i ■•  lA*_.  Ij'  j ■'■  fel  *«. 

‘‘**^*''  a^,Tim  iMifWi^yj  I *riit-ieKyjwqpk’,>Ma>^ 


r- 

me  - 


wJi  •. 


-54- 


weights  in  shoots  of  seedlings  grown  under  different  conditions 
of  moisture,  the  results  presented  in  Tables  V,  VI  and  XVI 
jtiDEjt  accord  with  the  results  obtained  by  previous  investigators. 
Sorauer  ('81),  Gain  ('95),  Wollny  ('98),  Pagnoul  ('99)  and 
Prianishnikov  ('00)  observed  that  as  the  per  cent  of  water  in 
the  soil  was  increased  the  per  cent  of  dry  matter  in  the  plants 
decreased.  Their  results,  as  reported,  are  consistent  and  in 
some  cases  marked  differences  were  obtained.  Some  slight  in- 
consistencies are  shown  in  Tables  V and  VI,  but  on  the  whole  a 
distinct  relation  between  the  amount  of  water  present  in  the 
soil  or  in  the  atmosphere  and  the  per  cent  of  dry  matter  present 
in  the  plant  exists.  The  difference  is  more  striking  in  the 
seedlings  grown  under  part  time  illumination  than  in  the  seed- 
lings grown  4n  continuous  darkness.  The  observations  on  the 
illuminated  seedlings  agree  more  closely,  as  would  be  expected, 
with  the  observations  of  the  investigators  mentioned.  The  higher 
percentage  of  dry  matter  occurring  in  the  seedlings  grown  under 
the  less  favorable  moisture  conditions  are  due,  undoubtedly,  to 
a greater  development  of  strengthening  tissue,  as  demonstrated 
by  Kohl (» 86)  and  Wollny  ('98). 

It  has  been  shown  that  soil  moisture  and  relative 
humidity  play  a part  in  determining  the  total  increment  of  elonga- 
tion in  plant  shoots.  The  data  presented  in  Tables  II  and  III 
indicate  that  a soil  very  low  in  moisture  provides  less  favorable 
conditions  for  longitudinal  growth  in  plant  shoots  than  a soil 


-55- 


high  in  moisture.  The  single  exception  to  this  has  already 
been  noted.  With  this  one  eiiception,  the  increases  in  the 
td)tal  increments  occurring  in  soil  moistures  of  30  per  cent 
saturation  and  60  per  cent  si-turation,  as  shown  in  Tables  XI 
and  XII,  are  not  unlike  those  obtained  by  Sorauer  ('73),  Hell- 
riegel  ('83),  Gain  ('93),  Wollny  ('97),  Seelhorst  COO),  Hunger 
('06)  and  others.  Their  results  differ  from  those  presented  in 
the  tables  referred  to^ however,  in  that  increases  in  total 
elongation  were  obtained  in  soil  moistures  much  above  20  per 
cent  saturation.  It  is  true  that  in  the  present  investigation 
soil  moisture3between  30  per  cent  and  60  per  cent  saturation 
were  not  employed.  It  is,  possible,  therefore,  that  a soil 
moisture,  intermediate  between  these  two,  would  provide  more 
favorable  conditions  for  elongation  in  shoots  than  those  em- 
ployed. A definite  answer  to  this  Awaits  further  invest igatioh. 
The  fact  that  in  the  researches  referred  to  the  plants  were 
grown  in  light,  while  the  seedlings  furnishing  the  data  presented 
in  the  tables  indicated  were  grown  in  darkness,  may  account  for 
this  discrepancy. 

With  reference  to  the  exception  noted  above  close 

inspection  of  the  tables  suggests  that  this  value  does  not  truly 

in 

represent  the  total  increment  for  the  seedlings  falling^that 
group.  This  wide  difference  is  due  possibly  to  chance.  If 
this  experiment  were  repeated  fifty  or  a hundred  times,  it  is 
probable  that  in  eveyy  case  the  value  would  approach  more  nearly 


1;  f.  ■ ■ . ;.rva^,■■;Vi^  ,v^ 

. ; 

■ •'■  .V '■'  ::■ 


- -i 


t . 


, f:  ' 

.'f  e-rt0‘ . 


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*uVV*5  ,*'»• 


. {.L- 

L.f,  ., 


^ i 1 • ' ' ' t W.  ' 


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-’  ; 

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vf' 

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,\  i'Hm  ■■■.',  ',  vi 


'4(\‘  • » ' J..  . 


'.  :,  r:,.i  V • :: 

■'  ' 

. :'r.-rj*  i'>.  , r,- V" 

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> ^ t '■ 


a;’.' 


u 

■ J ' f,  sv  *. 


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t . 


?«t 


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Att  '. 'v,[i 


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if*Vt 


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■ ' . ' ''^'  . ;„ 


. )'  „'..  ' ' 


-56- 


the  values  of  the  seedlings  in  the  neighboring  groups. 

In  respect  to  the  effeot  of  relative  humidity  on  the 
total  length  of  shoots,  the  researches  of  Reinitzer  (’81), 

Wollny  ('98),  Eberhardt  ('03,  '04)  and  others  are  confirmed  by 
certain  of  the  data  presented  in  this  paper.  The  number  of  cases 
in  which  relative  humidity  has  brought  about  a significant  differ- 
ence in  the  total  increment  of  elongation,  however,  is  too 
small  to  place  much  reliance  on  relative  humidity,  within  the 
limits  of  that  commonly  occurring  in  nature,  being  an  important 
factor  in  determining  the  total  length  of  plant  shoots. 

In  presenting  the  data,  attention  was  called  to  the 
differenoes  in  the  rate  of  elongation  between  the  seedlings 
grown  in  darkness  and  those  grown  in  part  time  illumination. 

As  already  indicated,  the  differences  are  very  significant. 

Light  decreased  not  only  the  rate  of  gro\7th,  but  also  the  total 
increment  of  growth  made  during  the  period  of  observation.  This 
agrees  with  the  conclusions  reached  by  Prantl  ('73),  Sachs  ('74), 
Stebler  ('78),  Barenetsky  ('79),  Godlewski  ('91)  and  others. 

On  the  other  hand,  the  observations  of  Meyer  ('28),  Maxwell 
('96),  Vog®  ('15)  and  others  do  not  accord  with  the  results  re- 
ported in  this  paper.  In  seedlings  of  sunflower,  growing  in 
the  free  air,  Reinke  ('76)  observed  that  growth  took  place  more 
rapidly  by  night  than  by  day.  Where  relative  humidity  was  main- 
tained constant,  however,  he  observed  a more  rapid  growh  in 
light  than  in  darkness.  It  is  difficult  to  account  for  the 


: \'  • 


m , 

><:  -i 


^■:  : V:-^  ,u  .•  C>~  ..  . I 


- ( • ' / ' 
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■■■>''  -'  • _ ■ 

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■■  . f 

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, t ..  VO,  * ' . i <v.  ^ 


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l.-'v  ..  I 


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rtf- 


'a  .,‘«V^  'O^v'A'  t ^ ^ ■ -:.W 


.:*!!;  i.:,: 


'11  ' 

¥ .a  V— - >■  • 


''■•./■,  • ■ ■ - '1  ■■  ■ 

:'y>.  'i,  :..X  ■ ''  u'  /•*•'  .•:  r ^ ... 

' X ' r ...  ..  ,....■,;  'i:C  . 


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- ••- ^ 1— .i-^t -T'  ' ■ ■ '•  .■  .'k.V.A' A‘;\'-  «*-Vj  -rff!.'-  ■■  : IV  ■ — V*  I U V.-:.  A*siW<MAVi~''“:.7?=>t.'‘' . T : fl 


-57- 


wide  differences  in  the  results  obtained  by  the  various  investi- 
gators. Mention  may  be  made  of  the  fact  that  Reinke  based  his 
conclusions  upon  the  results  obtained  from  one  or  two  plants. 

The  uncertainties  in  drawing  conclusions  from  few  individuals 
have  already  been  pointed  out^  and  it  is  probable  that  some  of 
the  discrepancies  may  be  accounted  for  through  differences  in 
the  number  of  cultures  employed.  In  some  cases,  the  differences 
obtained  between  plants  growing  in  light  and  plants  growing  in 
darkness  were  ascribed  to  the  presence  of  light  or  to  the  ab- 
sence of  light,  while  other  factors  w^re  disregarded.  Under 
such  circumstances  lack  of  consistency  in  the  results  obtained 
may  be  expected.  However,  the  evidence  brought  forth  in  this 
paper  that  light  has  a retarding  effect  upon  growth  should 
stimulate  further  investigation  in  this  field. 

The  observations  in  this  investigation  on  the  character 
of  the  root  systems  found  on  seedlings  growing  in  soils  of  differ 
ent  moisture  content  do  not  agree  with  those  of  Gain  ('S5). 

This  author  states,  "L'humidite  du  sol  parait  ralenter  la 
croissance  terminals  de  la  racine  principals,  et  exagerer  la 
croissance  dee  ramifications  secondaires  et  tertiaires.  Ces 
resultats  sent  inverses  de  ceux  qui  on  observe  sur  la  tige.” 

Gain  based  this  statement  upon  observations  made  on  plants  of 
buckwheat.  Observations  on  seedlings  grown  in  this  laboratory 
indicate  that,  under  a given  set  of  conditions,  plants  differ 
in  respect  to  the  type  of  root  system  produced.  This  may 


account  for  the 


■•"■*  .,*«•  J 


-58- 


differences  obtained.  It  is  probable  also  that  differences 
in  the  nature  of  the  soil  will  prove  an  important  factor  for 
consideration  in  accotlnting  for  this  discrepancy. 

Aside  from  their  importance  to  the  botanist^the  re- 
sults obtained  in  this  investigation  give  promise  of  much  worth 
to  the  agriculturist.  Definite  values  from  the  agriculturist’s 
viewpoint  cannot  be  assigned  to  them,  however,  until  further 
researches  are  made.  In  assigning  to  them  a value  it  must  not 
be  overlooked  that  this  investigation  was  confined  to  a study 
of  plants  of  the  common  bean  in  the  seedling  stage.  Giving 
this  due  consideration,  the  results  already  obtained  are 
suggestive  and  give  some  indication  of  what  may  be  expected 
from  plants  in  the  more  advanced  stages  of  growth. 

If  plants  of  other  species,  growing  under  natural 
conditions,  prove  to  respond  to  moisture  in  a manner  similar 
to  that  of  seedlings  of  the  common  bean,  the  results  obtained 
in  this  investigation  will  have  wide  application.  If  these 
results  apply  universally^,  relative  humidity  and  the  evaporat- 
ing pov/er  of  the  air  may,  in  a large  measure,  be  disregarded. 

The  moisture  of  tjie  soil,  on  the  other  hand,  must  receive  greater 
attention.  In  the  irrigated  districts  the  relative  humidity  is 
lowland  little  may  be  done  toward  increasing  it.  The  water  of 
the  soil,  on  the  other  hand,  may  be  increased  readily  and  any 
desired  per  cent  of  saturation  obtained.  In  districts  where 
irrigation  is  not  practiced  and  where  the  supply  of  soil  mois- 
ture depends  largely  upon  the  precipitation,  greater  attention 


-59- 


to  the  conservation  of  that  moisture  may  he  given.  Briggs 
and  Shantz  (*13,  *14)  have  shown  that  farm  crops,  producing 
an  average  yield,  require  from  6 to  18  acre  inches  of  water 
for  the  completion  of  growth.  Except  in  arid  regions  the 
annual  precipitation  greatly  exceeds  that  required  for  the 
production  of  a crop.  By  employing  the  most  improved  methods 
of  cultivation,  the  loss  of  moisture  from  the  soil  ^ay  be  re- 
duced to  a minimum  and  the  conditions  for  plant  growth  thereby 
improved.  In  the  greenhouse,  except  in  special  cases,  the 
relative  humidity  of  the  atmosphere  may  receive  less  attention^ 
while  more  attention  is  given  to  soil  water.  Through  a more 
favorable  supply  of  soil  moisture  the  harmful  effects  high 
rates  of  evaporation  and  transpiration,  brought  about  by  low 
relative  humidities  and  warm  winds  may,  in  a measure,  be  over- 
come. 

VIII.  SUMMARY. 


1.  Elongation  in  etiolated  shoots  of  seedlings  of 

the  common  bean,  growing  in  a pure  silica  sand  either  20  per 

e 

cent  or  60  per  cent  saturated  with  water,  preceded  rapidly 
in  a relative  humidity  of  30  per  cent  as  in  a relative  humidity 
of  either  60  per  cent  or  90  per  cent. 

2.  The  shoots  of  etiolated  bean  seedlings  growing 

in  a pure  silica  sand  5 per  cent  saturated  elongated  less  rapid- 


.r-,. : ■■  ■vi  •,«! 


.i  , " 


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V ' ^ ^ f * ■ t*‘  * * - 

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rjvvc/ijf' 

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VI 


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-r.  I.. 


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-U'  r. , ;...  ■ , •'.  ' lid  Vk.  '■  C- 


. •!?*  i.'l'iC 

a''’'-'i,‘ 


^_  «-Ot  S 


:;«V^  ... ; ...J!  i o: 


• • j ^ f :•  .•./.•^^.o.ii^3;»  JBjjf  f*'  .brjVpi  i :!  1 


■I  ' • .'/■  " ' 


■•  ■',  ; •’  'om'. 

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v<y  ■■: 


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f'*. 


jS 


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\’  ' J*''  it'* j 


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10'  *:  • . ■ i 

J ^ y I t II  - - *i  _i.  ‘ * • , •*■  •'»*»•  f • : 

L:J^>  • ~ 4%  . j.  . ^ t.  f\  / 

'■''  ■ , ^ 


^ i-  , ■ ‘ ‘ . V , " ' ^ _L_^  fV 

.' ■',  Ai'  •>' t'.".  >i4v  .S 


> ‘U 

* '•■  ’ 


“ ^ .V 


.v  ';,.;r;.  ..‘•^,  t 


„ c x._  / '••..y,?:.:^r4  - 

V ■ '^.  •■  V-  ■ ■ . ; '- 


’'■-.t  'Pt  Tx 


.^iVDo,  i-‘^’ . ’:v> 


:q 


.■U- 


V V ••  4 


Li' 


4 , 


■•'ill.. 


r'lf  , V 


yirx‘ 

■ ' . ^ . • ■ 

» •'  •* 

•'^^  rjl  • 'Yi 

'■'.I'x:  ;f'  .,  ,,' 

U Ur> 

" " M}/  \ 

* - -■  -ii-snik  : V. 

-60- 


ly  in  a relative  hiujidity  of  30  per  cent  than  in  relative 
humidities  of  60  per  cent  and  90  per  cent. 

3.  In  a pure  silica  sand  5 per  cent  saturated,  the 
shoots  of  etiolated  bean  seedlings  elongated  as  rapidly  in  a 
relative  humidity  of  60  per  cent  as  in  a relative  humidity  of 
90  per  cent. 

4.  The  rate  of  elongation  in  shoots  of  bean  seedlings 
growing  in  darkness  alternating  with  light  appears  to  be  in- 
fluenced by  relative  humidity  in  a manner  not  \inlike  that  in 
shoots  of  similar  seedlings  growing  in  continuous  darkness. 

5.  The  shoots  of  bean  seedlings  growing  in  darkness 
alternating  with  light  elongate  less  rapidly  than  the  shoots  of 
similar  seedlings  growing  in  continuous  darkness. 

6.  In  the  presence  of  both  high  and  low  relative 
humidities_,  etiolated  bean  seedlings  elongate  more  rapidly  in 

a silica  sand  20  per  cent  saturated  with  water  than  in  a silica 
sand  5 per  cent  saturated  with  water.  In  a sand  60  per  cent 
saturated^ the  rate  of  elongation  approaches  that  in  a sand  20 
per  cent  saturated. 

7.  The  per  cent  of  dry  matter  in  the  plant  varies 
inversely  as  the  soil  moisture  and  the  relative  humidity. 

8.  Significant  changes  in  the  relation  between  the 
dry  weights  of  roots  and  the  dry  weights  of  shoots  were  not 
brought  about  by  increasing  the  soil  water  from  5 per  cent 
saturation  to  60  per  cent  saturation. 


I '■  ,<4. 

n 


f *^'  rj  ^ ‘^^'1 

y 'y\v  .j__  " 


VM  :^1- >1.  v^'. . - •®  «...  La  . ^ ;'^&.  1 «■  . 


'V  2 -if '.  : • '*'•>.%'■■  ■■  ' . ■ -a.  T'. :,  .f-^fr>yy-:T.#1irafl  - 'V  ■ 


■-.|r»«^  r ■ 


■ - I . ki^f^  i vnjji  J5^  ./ .,♦?  i ?L«ai-'i'  ,f  ^-a<)lSSX<«^  V# 


S-  ir^.’.- * ''  V J Y *'  5'!^-  V < fjlTa^  _fjpA*  ^ ^ S"'  ' 

u '■  ■ < ^-ji&sfc. ,•'■  iCvi ! ii'CS, -ix  '^SSt^K^Tl 


-61- 


IX.  CONCLUSIONS. 


1.  The  influence  of  relative  humidity  upon  growth 
in  higher  plants  has  been  greatly  overestimated. 

2.  In  studies  on  growth  in  relation  to  relative 
humidity,  the  available  moisture  in  the  substratum  must  be 
recognized  as  an  important  environmental  factor. 

3.  The  harmful  effects  of  low  relative  huijidity 
and  atmospheres  possessing  high  evaporating  coefficients  upon 
growth  in  plants,  may  be  overcome,  in  a large  measure,  by  main- 
taining an  abundance  of  moisture  in  the  substratum. 


‘ j:/"  w';''  'v'  - J>*'i''‘;/f^''‘*l^  "i 

m'Wv  ■ "■'  ' . - *'.•  '‘.^v^*l’^" . ^ .''•i'.  ,J"  - ■ ■ 

■ ' ^3  ■.  ■ ■,  ■ r " .-■''  : ,. ' V,  ■ ■■%'  .#  Jm' 


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i 


-68- 


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Wollny,  E 
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Wollny,  W 
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30:53-109. 


Untersuchungen  dber  den  Einflusg  der  Luftfeuohtig- 
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The  Interpretation  of  Experimental  Results. 

Jour.  Bd.  Ag.,  Great  Britain,  18,  Supplement  7:15-37. 


-73~ 


XI.  VITA. 

The  author  of  this  thesis  was  born  at  Watford, 
Ontario  on  December  1,  1892.  His  early  education  was 
received  in  the  secondary  schools  in  his  native  village. 
He  was  graduated  from  the  University  of  Toronto  with 
the  Degree  of  Bachelor  of  Scientific  Agriculture  in 
May,  1918.  In  January  1919,  he  entered  the  Graduate 
School  of  the  University  of  Illiinois  and  obtained  the 
Degree  of  Master  of  Science  in  March,  1920.  He  was 
registered  in  the  Graduate  School  of  this  University 
during  the  Summer  Session  of  1919  and  during  part  of 
the  Summer  Session  of  1920.  During  his  residence  at 
Illinois  he  has  devoted  full  time  to  study  for  an  ad- 
vanced degree. 


